Jim Tcl(n)
==========

NAME
----
Jim Tcl v0.80+ - reference manual for the Jim Tcl scripting language

SYNOPSIS
--------

  cc <source> -ljim

or

  jimsh [<scriptfile>|-]
  jimsh -e '<immediate-script>'
  jimsh --version
  jimsh --help


.Quick Index
* <<CommandIndex,Command Reference>>
* <<OperatorPrecedence,Operator Precedence>>
* <<BuiltinVariables, Builtin Variables>>
* <<BackslashSequences, Backslash Sequences>>

INTRODUCTION
------------
Jim Tcl is a small footprint reimplementation of the Tcl scripting language.
The core language engine is compatible with Tcl 8.5+, while implementing
a significant subset of the Tcl 8.6 command set, plus additional features
available only in Jim Tcl.

Some notable differences with Tcl 8.5/8.6/8.7 are:

1. Object-based I/O (aio), but with a Tcl-compatibility layer
2. I/O: Support for sockets and pipes including udp, unix domain sockets and IPv6
3. Integers are 64bit
4. Support for references (`ref`/`getref`/`setref`) and garbage collection
5. Builtin dictionary type (`dict`) with some limitations compared to Tcl 8.6
6. `env` command to access environment variables
7. Operating system features: `os.fork`, `os.uptime`, `wait`, `signal`, `alarm`, `sleep`
8. Much better error reporting. `info stacktrace` as a replacement for '$errorInfo', '$errorCode'
9. Support for "static" variables in procedures
10. Threads and coroutines are not supported
11. Command and variable traces are not supported
12. Built-in command line editing
13. Expression shorthand syntax: +$(...)+
14. Modular build allows many features to be omitted or built as dynamic, loadable modules
15. Highly suitable for use in an embedded environment
16. Support for UDP, IPv6, Unix-Domain sockets in addition to TCP sockets

RECENT CHANGES
--------------
Changes since 0.80
~~~~~~~~~~~~~~~~~~
1. TIP 582, comments allowed in expressions
2. Many commands now accept "safe" integer expressions rather than simple integers:
   `loop`, `range`, `incr`, `string repeat`, `lrepeat`, `pack`, `unpack`, `rand`
3. String and list indexes now accept integer expressions (<<_string_and_list_index_specifications,STRING AND LIST INDEX SPECIFICATIONS>>)
4. `loop` can now omit the start value
5. Add the `xtrace` command for execution trace support
6. Add `history keep`
7. Add support for `lsearch -index` and `lsearch -stride`, the latter per TIP 351
8. `lsort -index` now supports multiple indices
9. Add support for `lsort -stride`
10. `open` now supports POSIX-style access arguments
11. TIP 526, `expr` now only allows a single argument (unless --compat is enabled)

Changes between 0.79 and 0.80
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1. `regsub` now fully supports +{backslash}A+
2. Add `socket pty` to create a pseudo-tty pair
3. Null characters (\x00) are now supported in variable and proc names
4. dictionaries and arrays now preserve insertion order, matching Tcl and the documentation
5. Add `dict getwithdefault` (and the alias `dict getdef`) per TIP 342
6. Add string comparison operators (lt, gt, le, ge) per TIP 461
7. Implement 0d radix prefix for decimal per TIP 472

Changes between 0.78 and 0.79
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1. Add `file mtimeus` for high resolution file timestamps
2. `aio` now supports datagram Unix-Domain sockets
3. Add support for `aio lock -wait`
4. Add `signal block` to prevent delivery of signals
5. Add support for `file split`
6. Add support for `json::encode` and `json::decode`
7. `aio tty` now allows setting +echo+ without full +raw+ mode

Changes between 0.77 and 0.78
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1. Add serial/tty support with `aio tty`
2. Add support for 'jimsh -'
3. Add hidden '-commands' option to many commands
4. Add scriptable autocompletion support in interactive mode with `tcl::autocomplete`
5. Add `aio sockopt`
6. Add scriptable autocompletion support with `history completion`
7. Add support for `tree delete`
8. Add support for `defer` and '$jim::defer'
9. Renamed `os.wait` to `wait`, now more Tcl-compatible and compatible with `exec ... &`
10. `pipe` is now a synonym for `socket pipe`
11. Closing a pipe open with `open |...` now returns Tcl-like status
12. It is now possible to used `exec` redirection with a pipe opened with `open |...`
13. Interactive line editing now supports multiline mode if $::history::multiline is set

Changes between 0.76 and 0.77
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1. Add support for `aio sync`
2. Add SSL and TLS support in aio
3. Added `zlib`
4. Added support for boolean constants in `expr`
5. `string is` now supports 'boolean' class
6. Add support for `aio lock` and `aio unlock`
7. Add new `interp` command

Changes between 0.75 and 0.76
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1. `glob` now supports the +-tails+ option
2. Add support for `string cat`
3. Allow `info source` to add source info

Changes between 0.74 and 0.75
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1. `binary`, `pack` and `unpack` now support floating point
2. `file copy` +-force+ handles source and target as the same file
3. `format` now supports +%b+ for binary conversion
4. `lsort` now supports +-unique+ and +-real+
5. Add support for half-close with `aio close` +?r|w?+
6. Add `socket pair` for a bidirectional pipe
7. Add '--random-hash' to randomise hash tables for greater security
8. `dict` now supports 'for', 'values', 'incr', 'append', 'lappend', 'update', 'info' and 'replace'
9. `file stat` no longer requires the variable name
10. Add support for `file link`

TCL INTRODUCTION
-----------------
Tcl stands for 'tool command language' and is pronounced
'http://www.oxforddictionaries.com/definition/american_english/tickle[tickle]'.
It is actually two things: a language and a library.

First, Tcl is a simple textual language, intended primarily for
issuing commands to interactive programs such as text editors,
debuggers, illustrators, and shells.  It has a simple syntax and is also
programmable, so Tcl users can write command procedures to provide more
powerful commands than those in the built-in set.

Second, Tcl is a library package that can be embedded in application
programs.  The Tcl library consists of a parser for the Tcl language,
routines to implement the Tcl built-in commands, and procedures that
allow each application to extend Tcl with additional commands specific
to that application.  The application program generates Tcl commands and
passes them to the Tcl parser for execution.  Commands may be generated
by reading characters from an input source, or by associating command
strings with elements of the application's user interface, such as menu
entries, buttons, or keystrokes.

When the Tcl library receives commands it parses them into component
fields and executes built-in commands directly.  For commands implemented
by the application, Tcl calls back to the application to execute the
commands.  In many cases commands will invoke recursive invocations of the
Tcl interpreter by passing in additional strings to execute (procedures,
looping commands, and conditional commands all work in this way).

An application program gains three advantages by using Tcl for its command
language.  First, Tcl provides a standard syntax:  once users know Tcl,
they will be able to issue commands easily to any Tcl-based application.
Second, Tcl provides programmability.  All a Tcl application needs
to do is to implement a few application-specific low-level commands.
Tcl provides many utility commands plus a general programming interface
for building up complex command procedures.  By using Tcl, applications
need not re-implement these features.

Third, Tcl can be used as a common language for communicating between
applications.  Inter-application communication is not built into the
Tcl core described here, but various add-on libraries, such as the Tk
toolkit, allow applications to issue commands to each other.  This makes
it possible for applications to work together in much more powerful ways
than was previously possible.

Fourth, Jim Tcl includes a command processor, +jimsh+, which can be
used to run standalone Tcl scripts, or to run Tcl commands interactively.

This manual page focuses primarily on the Tcl language.  It describes
the language syntax and the built-in commands that will be available
in any application based on Tcl.  The individual library procedures are
described in more detail in separate manual pages, one per procedure.

JIMSH COMMAND INTERPRETER
-------------------------
A simple, but powerful command processor, +jimsh+, is part of Jim Tcl.
It may be invoked in interactive mode as:

  jimsh

or to process the Tcl script in a file with:

  jimsh filename

or to process the Tcl script from standard input:

  jimsh -

It may also be invoked to execute an immediate script with:

  jimsh -e "script"

Interactive Mode
~~~~~~~~~~~~~~~~
Interactive mode reads Tcl commands from standard input, evaluates
those commands and prints the results.

  $ jimsh
  Welcome to Jim version 0.73, Copyright (c) 2005-8 Salvatore Sanfilippo
  . info version
  0.73
  . lsort [info commands p*]
  package parray pid popen proc puts pwd
  . foreach i {a b c} {
  {> puts $i
  {> }
  a
  b
  c
  . bad
  invalid command name "bad"
  [error] . exit
  $

If +jimsh+ is configured with line editing (it is by default) and a VT-100-compatible
terminal is detected, Emacs-style line editing commands are available, including:
arrow keys, +\^W+ to erase a word, +\^U+ to erase the line, +^R+ for reverse incremental search
in history. Additionally, the +h+ command may be used to display the command history.

Command line history is automatically saved and loaded from +~/.jim_history+

In interactive mode, +jimsh+ automatically runs the script +~/.jimrc+ at startup
if it exists.

INTERPRETERS
------------
The central data structure in Tcl is an interpreter (C type 'Jim_Interp').
An interpreter consists of a set of command bindings, a set of variable
values, and a few other miscellaneous pieces of state.  Each Tcl command
is interpreted in the context of a particular interpreter.

Some Tcl-based applications will maintain multiple interpreters
simultaneously, each associated with a different widget or portion of
the application.  Interpreters are relatively lightweight structures.
They can be created and deleted quickly, so application programmers should
feel free to use multiple interpreters if that simplifies the application.

DATA TYPES
----------
Tcl supports only one type of data:  strings.  All commands, all arguments
to commands, all command results, and all variable values are strings.

Where commands require numeric arguments or return numeric results,
the arguments and results are passed as strings.  Many commands expect
their string arguments to have certain formats, but this interpretation
is up to the individual commands.  For example, arguments often contain
Tcl command strings, which may get executed as part of the commands.
The easiest way to understand the Tcl interpreter is to remember that
everything is just an operation on a string.  In many cases Tcl constructs
will look similar to more structured constructs from other languages.
However, the Tcl constructs are not structured at all; they are just
strings of characters, and this gives them a different behaviour than
the structures they may look like.

Although the exact interpretation of a Tcl string depends on who is doing
the interpretation, there are three common forms that strings take:
commands, expressions, and lists.  The major sections below discuss
these three forms in more detail.

BASIC COMMAND SYNTAX
--------------------
The Tcl language has syntactic similarities to both the Unix shells
and Lisp.  However, the interpretation of commands is different
in Tcl than in either of those other two systems.
A Tcl command string consists of one or more commands separated
by newline characters or semi-colons.
Each command consists of a collection of fields separated by
white space (spaces or tabs).
The first field must be the name of a command, and the
additional fields, if any, are arguments that will be passed to
that command.  For example, the command:

----
    set a 22
----

has three fields:  the first, `set`, is the name of a Tcl command, and
the last two, 'a' and '22', will be passed as arguments to
the `set` command.  The command name may refer either to a built-in
Tcl command, an application-specific command bound in with the library
procedure 'Jim_CreateCommand', or a command procedure defined with the
`proc` built-in command.

Arguments are passed literally as text strings.  Individual commands may
interpret those strings in any fashion they wish.  The `set` command,
for example, will treat its first argument as the name of a variable
and its second argument as a string value to assign to that variable.
For other commands arguments may be interpreted as integers, lists,
file names, or Tcl commands.

Command names should normally be typed completely (e.g. no abbreviations).
However, if the Tcl interpreter cannot locate a command it invokes a
special command named `unknown` which attempts to find or create the
command.

For example, at many sites `unknown` will search through library
directories for the desired command and create it as a Tcl procedure if
it is found.  The `unknown` command often provides automatic completion
of abbreviated commands, but usually only for commands that were typed
interactively.

It's probably a bad idea to use abbreviations in command scripts and
other forms that will be re-used over time:  changes to the command set
may cause abbreviations to become ambiguous, resulting in scripts that
no longer work.

COMMENTS
--------
If the first non-blank character in a command is +\#+, then everything
from the +#+ up through the next newline character is treated as
a comment and ignored.  When comments are embedded inside nested
commands (e.g. fields enclosed in braces) they must have properly-matched
braces (this is necessary because when Tcl parses the top-level command
it doesn't yet know that the nested field will be used as a command so
it cannot process the nested comment character as a comment).

GROUPING ARGUMENTS WITH DOUBLE-QUOTES
-------------------------------------
Normally each argument field ends at the next white space, but
double-quotes may be used to create arguments with embedded space.

If an argument field begins with a double-quote, then the argument isn't
terminated by white space (including newlines) or a semi-colon (see below
for information on semi-colons); instead it ends at the next double-quote
character.  The double-quotes are not included in the resulting argument.
For example, the command

----
    set a "This is a single argument"
----

will pass two arguments to `set`:  'a' and 'This is a single argument'.

Within double-quotes, command substitutions, variable substitutions,
and backslash substitutions still occur, as described below.  If the
first character of a command field is not a quote, then quotes receive
no special interpretation in the parsing of that field.

GROUPING ARGUMENTS WITH BRACES
------------------------------
Curly braces may also be used for grouping arguments.  They are similar
to quotes except for two differences.  First, they nest; this makes them
easier to use for complicated arguments like nested Tcl command strings.
Second, the substitutions described below for commands, variables, and
backslashes do *not* occur in arguments enclosed in braces, so braces
can be used to prevent substitutions where they are undesirable.

If an argument field begins with a left brace, then the argument ends
at the matching right brace.  Tcl will strip off the outermost layer
of braces and pass the information between the braces to the command
without any further modification.  For example, in the command

----
    set a {xyz a {b c d}}
----

the `set` command will receive two arguments: 'a'
and 'xyz a {b c d}'.

When braces or quotes are in effect, the matching brace or quote need
not be on the same line as the starting quote or brace; in this case
the newline will be included in the argument field along with any other
characters up to the matching brace or quote.  For example, the `eval`
command takes one argument, which is a command string; `eval` invokes
the Tcl interpreter to execute the command string.  The command

----
    eval {
      set a 22
      set b 33
    }
----

will assign the value '22' to 'a' and '33' to 'b'.

If the first character of a command field is not a left
brace, then neither left nor right
braces in the field will be treated specially (except as part of
variable substitution; see below).

COMMAND SUBSTITUTION WITH BRACKETS
----------------------------------
If an open bracket occurs in a field of a command, then command
substitution occurs (except for fields enclosed in braces).  All of the
text up to the matching close bracket is treated as a Tcl command and
executed immediately.  Then the result of that command is substituted
for the bracketed text.  For example, consider the command

----
    set a [set b]
----

When the `set` command has only a single argument, it is the name of a
variable and `set` returns the contents of that variable.  In this case,
if variable 'b' has the value 'foo', then the command above is equivalent
to the command

----
    set a foo
----

Brackets can be used in more complex ways.  For example, if the variable
'b' has the value 'foo' and the variable 'c' has the value 'gorp',
then the command

----
    set a xyz[set b].[set c]
----

is equivalent to the command

----
    set a xyzfoo.gorp
----

A bracketed command may contain multiple commands separated by newlines
or semi-colons in the usual fashion.  In this case the value of the last
command is used for substitution.  For example, the command

----
    set a x[set b 22
    expr $b+2]x
----

is equivalent to the command

----
    set a x24x
----

If a field is enclosed in braces then the brackets and the characters
between them are not interpreted specially; they are passed through to
the argument verbatim.

VARIABLE SUBSTITUTION WITH $
----------------------------
The dollar sign (+$+) may be used as a special shorthand form for
substituting variable values.  If +$+ appears in an argument that isn't
enclosed in braces then variable substitution will occur.  The characters
after the +$+, up to the first character that isn't a number, letter,
or underscore, are taken as a variable name and the string value of that
variable is substituted for the name.

For example, if variable 'foo' has the value 'test', then the command

----
    set a $foo.c
----

is equivalent to the command

----
    set a test.c
----

There are two special forms for variable substitution.  If the next
character after the name of the variable is an open parenthesis, then
the variable is assumed to be an array name, and all of the characters
between the open parenthesis and the next close parenthesis are taken as
an index into the array.  Command substitutions and variable substitutions
are performed on the information between the parentheses before it is
used as an index.

For example, if the variable 'x' is an array with one element named
'first' and value '87' and another element named '14' and value 'more',
then the command

----
    set a xyz$x(first)zyx
----

is equivalent to the command

----
    set a xyz87zyx
----

If the variable 'index' has the value '14', then the command

----
    set a xyz$x($index)zyx
----

is equivalent to the command

----
    set a xyzmorezyx
----

For more information on arrays, see <<_variables_scalars_and_arrays,VARIABLES - SCALARS AND ARRAYS>> below.

The second special form for variables occurs when the dollar sign is
followed by an open curly brace.  In this case the variable name consists
of all the characters up to the next curly brace.

Array references are not possible in this form:  the name between braces
is assumed to refer to a scalar variable.  For example, if variable
'foo' has the value 'test', then the command

----
    set a abc${foo}bar
----

is equivalent to the command

----
    set a abctestbar
----


Variable substitution does not occur in arguments that are enclosed in
braces:  the dollar sign and variable name are passed through to the
argument verbatim.

The dollar sign abbreviation is simply a shorthand form.  +$a+ is
completely equivalent to +[set a]+; it is provided as a convenience
to reduce typing.

SEPARATING COMMANDS WITH SEMI-COLONS
------------------------------------
Normally, each command occupies one line (the command is terminated by a
newline character).  However, semi-colon (+;+) is treated as a command
separator character; multiple commands may be placed on one line by
separating them with a semi-colon.  Semi-colons are not treated as
command separators if they appear within curly braces or double-quotes.

BACKSLASH SUBSTITUTION
----------------------
Backslashes may be used to insert non-printing characters into command
fields and also to insert special characters like braces and brackets
into fields without them being interpreted specially as described above.

The backslash sequences understood by the Tcl interpreter are
listed below.  In each case, the backslash
sequence is replaced by the given character:
[[BackslashSequences]]
+{backslash}b+::
    Backspace (0x8)

+{backslash}f+::
    Form feed (0xc)

+{backslash}n+::
    Newline (0xa)

+{backslash}r+::
    Carriage-return (0xd).

+{backslash}t+::
    Tab (0x9).

+{backslash}v+::
    Vertical tab (0xb).

+{backslash}{+::
    Left brace ({).

+{backslash}}+::
    Right brace (}).

+{backslash}[+::
    Open bracket ([).

+{backslash}]+::
    Close bracket (]).

+{backslash}$+::
    Dollar sign ($).

+{backslash}<space>+::
    Space ( ): doesn't terminate argument.

+{backslash};+::
    Semi-colon: doesn't terminate command.

+{backslash}"+::
    Double-quote.

+{backslash}<newline>+::
    Nothing:  this joins two lines together
    into a single line.  This backslash feature is unique in that
    it will be applied even when the sequence occurs within braces.

+{backslash}{backslash}+::
    Backslash ('{backslash}').

+{backslash}ddd+::
    The digits +'ddd'+ (one, two, or three of them) give the octal value of
    the character.  Note that Jim supports null characters in strings.

+{backslash}unnnn+::
+{backslash}u\{nnn\}+::
+{backslash}Unnnnnnnn+::
    The UTF-8 encoding of the unicode codepoint represented by the hex digits, +'nnnn'+, is inserted.
    The 'u' form allows for one to four hex digits.
    The 'U' form allows for one to eight hex digits.
    The 'u\{nnn\}' form allows for one to eight hex digits, but makes it easier to insert
    characters UTF-8 characters which are followed by a hex digit.

For example, in the command

----
    set a \{x\[\ yz\141
----

the second argument to `set` will be +{x[ yza+.

If a backslash is followed by something other than one of the options
described above, then the backslash is transmitted to the argument
field without any special processing, and the Tcl scanner continues
normal processing with the next character.  For example, in the
command

----
    set \*a \\\{foo
----

The first argument to `set` will be +{backslash}*a+ and the second
argument will be +{backslash}{foo+.

If an argument is enclosed in braces, then backslash sequences inside
the argument are parsed but no substitution occurs (except for
backslash-newline):  the backslash
sequence is passed through to the argument as is, without making
any special interpretation of the characters in the backslash sequence.
In particular, backslashed braces are not counted in locating the
matching right brace that terminates the argument.
For example, in the
command

----
    set a {\{abc}
----

the second argument to `set` will be +{backslash}{abc+.

This backslash mechanism is not sufficient to generate absolutely
any argument structure; it only covers the
most common cases.  To produce particularly complicated arguments
it is probably easiest to use the `format` command along with
command substitution.

STRING AND LIST INDEX SPECIFICATIONS
------------------------------------

Many string and list commands take one or more 'index' parameters which
specify a position in the string relative to the start or end of the string/list.

The index may be one of the following forms:

+integer+::
    A simple integer, where +0+ refers to the first element of the string
    or list.

+integerexpression+::
    Any "safe" expression that evaluates to an integer. A "safe" expression does not perform
    variable or command subsitution, but is otherwise like a normal expression
    (see <<_expressions,EXPRESSIONS>>).

 ::
    For example +1+2*3+ is valid integer expression, but +{$x*2-1}+ is not.
    But note that it is possible to use an unbraced expression to allow the Tcl interpreter
    to expand variables and commands before being parsed as an integer expression.

 ::
    e.g. +string repeat a $x*2-1+

+*end*+::
    The last element of the string or list.

+*end*-integer+::
+*end*-integerexpression+::
+*end*+integerexpression+::
    The 'nth-from-last' element of the string or list. Again, a "safe" integer expression
    may be used in place of a simple integer. +end-3+ or  +end-3+2*$n+. Normally it only makes
    sense to use the +*end*-+ form, but if the integer expression is negative, the +*end*++ form
    may be used.

COMMAND SUMMARY
---------------
1. A command is just a string.
2. Within a string commands are separated by newlines or semi-colons
   (unless the newline or semi-colon is within braces or brackets
   or is backslashed).
3. A command consists of fields.  The first field is the name of the command.
   The other fields are strings that are passed to that command as arguments.
4. Fields are normally separated by white space.
5. Double-quotes allow white space and semi-colons to appear within
   a single argument.
   Command substitution, variable substitution, and backslash substitution
   still occur inside quotes.
6. Braces defer interpretation of special characters.
   If a field begins with a left brace, then it consists of everything
   between the left brace and the matching right brace. The
   braces themselves are not included in the argument.
   No further processing is done on the information between the braces
   except that backslash-newline sequences are eliminated.
7. If a field doesn't begin with a brace then backslash,
   variable, and command substitution are done on the field.  Only a
   single level of processing is done:  the results of one substitution
   are not scanned again for further substitutions or any other
   special treatment.  Substitution can
   occur on any field of a command, including the command name
   as well as the arguments.
8. If the first non-blank character of a command is a +\#+, everything
   from the +#+ up through the next newline is treated as a comment
   and ignored.

EXPRESSIONS
-----------
The second major interpretation applied to strings in Tcl is
as expressions.  Several commands, such as `expr`, `for`,
and `if`, treat one or more of their arguments as expressions
and call the Tcl expression processors ('Jim_ExprLong',
'Jim_ExprBoolean', etc.) to evaluate them.

The operators permitted in Tcl expressions are a subset of
the operators permitted in C expressions, and they have the
same meaning and precedence as the corresponding C operators.
Expressions almost always yield numeric results
(integer or floating-point values).
For example, the expression

----
    8.2 + 6
----

evaluates to 14.2.

Tcl expressions differ from C expressions in the way that
operands are specified, and in that Tcl expressions support
non-numeric operands and string comparisons.

A Tcl expression consists of a combination of operands, operators,
and parentheses.

White space may be used between the operands and operators and
parentheses; it is ignored by the expression processor.
Where possible, operands are interpreted as integer values.

Comments are allowed in expressions, beginning with the '#' character
and continuing until the end of line or end of expression.

Integer values are interpreted as decimal, binary, octal or
hexadecimal if prepended with '0d', '0b', '0o' or '0x'
respectively. Otherwise they are interpreted as decimal by default.
(Jim Tcl does not interpret numbers with leading zeros as octal.)

If an operand does not have one of the integer formats given
above, then it is treated as a floating-point number if that is
possible.  Floating-point numbers may be specified in any of the
ways accepted by an ANSI-compliant C compiler (except that the
'f', 'F', 'l', and 'L' suffixes will not be permitted in
most installations).  For example, all of the
following are valid floating-point numbers:  2.1, 3., 6e4, 7.91e+16.

If no numeric interpretation is possible, then an operand is left
as a string (and only a limited set of operators may be applied to
it).

String constants representing boolean constants
(+'0'+, +'1'+, +'false'+, +'off'+, +'no'+, +'true'+, +'on'+, +'yes'+)
are also recognized and can be used in logical operations.

1. Operands may be specified in any of the following ways:

2. As a numeric value, either integer or floating-point.

3. As one of valid boolean constants

4. As a Tcl variable, using standard '$' notation.
The variable's value will be used as the operand.

5. As a string enclosed in double-quotes.
The expression parser will perform backslash, variable, and
command substitutions on the information between the quotes,
and use the resulting value as the operand

6. As a string enclosed in braces.
The characters between the open brace and matching close brace
will be used as the operand without any substitutions.

7. As a Tcl command enclosed in brackets.
The command will be executed and its result will be used as
the operand.

Where substitutions occur above (e.g. inside quoted strings), they
are performed by the expression processor.
However, an additional layer of substitution may already have
been performed by the command parser before the expression
processor was called.

As discussed below, it is usually best to enclose expressions
in braces to prevent the command parser from performing substitutions
on the contents.

For some examples of simple expressions, suppose the variable 'a' has
the value 3 and the variable 'b' has the value 6.  Then the expression
on the left side of each of the lines below will evaluate to the value
on the right side of the line:

----
    $a + 3.1                6.1
    2 + "$a.$b"             5.6
    4*[llength "6 2"]       8
    {word one} < "word $a"  0
----

The valid operators are listed below, grouped in decreasing order
of precedence:
[[OperatorPrecedence]]
+int() double() round() abs(), rand(), srand()+::
    Unary functions (except rand() which takes no arguments)
    * +'int()'+ converts the numeric argument to an integer by truncating down.
    * +'double()'+ converts the numeric argument to floating point.
    * +'round()'+ converts the numeric argument to the closest integer value.
    * +'abs()'+ takes the absolute value of the numeric argument.
    * +'rand()'+ returns a pseudo-random floating-point value in the range (0,1).
    * +'srand()'+ takes an integer argument to (re)seed the random number generator. Returns the first random number from that seed.

+sin() cos() tan() asin() acos() atan() sinh() cosh() tanh() ceil() floor() exp() log() log10() sqrt()+::
    Unary math functions.
    If Jim is compiled with math support, these functions are available.

+- + ~ !+::
    Unary minus, unary plus, bit-wise NOT, logical NOT.  None of these operands
    may be applied to string operands, and bit-wise NOT may be
    applied only to integers.

+** pow(x,y)+::
    Power. e.g. 'x^y^'. If Jim is compiled with math support, supports doubles and
    integers. Otherwise supports integers only. (Note that the math-function form
    has the same highest precedence)

+* / %+::
    Multiply, divide, remainder.  None of these operands may be
    applied to string operands, and remainder may be applied only
    to integers.

++ -+::
    Add and subtract.  Valid for any numeric operands.

+<<  >> <<< >>>+::
    Left and right shift, left and right rotate.  Valid for integer operands only.

+<  >  \<=  >=+::
    Boolean less, greater, less than or equal, and greater than or equal.
    Each operator produces 1 if the condition is true, 0 otherwise.
    These operators may be applied to strings as well as numeric operands,
    in which case string comparison is used.

+lt  gt  le  ge+::
    Boolean less, greater, less than or equal, and greater than or equal.
    Each operator produces 1 if the condition is true, 0 otherwise.
    These operators differ from the above in that they use string comparison
    for all operands, including numeric.

+==  !=+::
    Boolean equal and not equal.  Each operator produces a zero/one result.
    Valid for all operand types. *Note* that values will be converted to integers
    if possible, then floating point types, and finally strings will be compared.
    It is recommended that 'eq' and 'ne' should be used for string comparison.

+eq ne+::
    String equal and not equal.  Uses the string value directly without
    attempting to convert to a number first.

+in ni+::
    String in list and not in list. For 'in', result is 1 if the left operand (as a string)
    is contained in the right operand (as a list), or 0 otherwise. The result for
    +{$a ni $list}+ is equivalent to +{!($a in $list)}+.

+&+::
    Bit-wise AND.  Valid for integer operands only.

+|+::
    Bit-wise OR.  Valid for integer operands only.

+^+::
    Bit-wise exclusive OR.  Valid for integer operands only.

+&&+::
    Logical AND.  Produces a 1 result if both operands are non-zero, 0 otherwise.
    Valid for numeric operands only (integers or floating-point).

+||+::
    Logical OR.  Produces a 0 result if both operands are zero, 1 otherwise.
    Valid for numeric operands only (integers or floating-point).

+x ? y : z+::
    If-then-else, as in C.  If +'x'+
    evaluates to non-zero, then the result is the value of +'y'+.
    Otherwise the result is the value of +'z'+.
    The +'x'+ operand must have a numeric value, while +'y'+ and +'z'+ can
    be of any type.

See the C manual for more details on the results
produced by each operator.
All of the binary operators group left-to-right within the same
precedence level.  For example, the expression

----
    4*2 < 7
----

evaluates to 0.

The +&&+, +||+, and +?:+ operators have 'lazy evaluation', just as
in C, which means that operands are not evaluated if they are not
needed to determine the outcome.  For example, in

----
    $v ? [a] : [b]
----

only one of +[a]+ or +[b]+ will actually be evaluated,
depending on the value of +$v+.

All internal computations involving integers are done with the C
type 'long long' if available, or 'long' otherwise, and all internal
computations involving floating-point are done with the C type
'double'.

When converting a string to floating-point, exponent overflow is
detected and results in a Tcl error.
For conversion to integer from string, detection of overflow depends
on the behaviour of some routines in the local C library, so it should
be regarded as unreliable.
In any case, overflow and underflow are generally not detected
reliably for intermediate results.

Conversion among internal representations for integer, floating-point,
string operands is done automatically as needed.
For arithmetic computations, integers are used until some
floating-point number is introduced, after which floating-point is used.
For example,

----
    5 / 4
----

yields the result 1, while

----
    5 / 4.0
    5 / ( [string length "abcd"] + 0.0 )
----

both yield the result 1.25.

String values may be used as operands of the comparison operators,
although the expression evaluator tries to do comparisons as integer
or floating-point when it can.
If one of the operands of a comparison is a string and the other
has a numeric value, the numeric operand is converted back to
a string using the C 'sprintf' format specifier
'%d' for integers and '%g' for floating-point values.
For example, the expressions

----
    "0x03" > "2"
    "0y" < "0x12"
----

both evaluate to 1.  The first comparison is done using integer
comparison, and the second is done using string comparison after
the second operand is converted to the string '18'.

In general it is safest to enclose an expression in braces when
entering it in a command:  otherwise, if the expression contains
any white space then the Tcl interpreter will split it
among several arguments.  For example, the command

----
    expr $a + $b
----

results in three arguments being passed to `expr`:  +$a+,
\+, and +$b+.  In addition, if the expression isn't in braces
then the Tcl interpreter will perform variable and command substitution
immediately (it will happen in the command parser rather than in
the expression parser).  In many cases the expression is being
passed to a command that will evaluate the expression later (or
even many times if, for example, the expression is to be used to
decide when to exit a loop).  Usually the desired goal is to re-do
the variable or command substitutions each time the expression is
evaluated, rather than once and for all at the beginning.  For example,
the command

----
    for {set i 1} $i<=10 {incr i} {...}        ** WRONG **
----

is probably intended to iterate over all values of +i+ from 1 to 10.
After each iteration of the body of the loop, `for` will pass
its second argument to the expression evaluator to see whether or not
to continue processing.  Unfortunately, in this case the value of +i+
in the second argument will be substituted once and for all when the
`for` command is parsed.  If +i+ was 0 before the `for`
command was invoked then the second argument of `for` will be +0\<=10+
which will always evaluate to 1, even though +i+ eventually
becomes greater than 10.  In the above case the loop will never
terminate.  Instead, the expression should be placed in braces:

----
    for {set i 1} {$i<=10} {incr i} {...}      ** RIGHT **
----

This causes the substitution of 'i'
to be delayed; it will be re-done each time the expression is
evaluated, which is the desired result.

LISTS
-----
The third major way that strings are interpreted in Tcl is as lists.
A list is just a string with a list-like structure
consisting of fields separated by white space.  For example, the
string

----
    Al Sue Anne John
----

is a list with four elements or fields.
Lists have the same basic structure as command strings, except
that a newline character in a list is treated as a field separator
just like space or tab.  Conventions for braces and quotes
and backslashes are the same for lists as for commands.  For example,
the string

----
    a b\ c {d e {f g h}}
----

is a list with three elements:  +a+, +b c+, and +d e {f g h}+.

Whenever an element is extracted from a list, the same rules about
braces and quotes and backslashes are applied as for commands.  Thus in
the example above when the third element is extracted from the list,
the result is

----
    d e {f g h}
----

(when the field was extracted, all that happened was to strip off
the outermost layer of braces).  Command substitution and
variable substitution are never
made on a list (at least, not by the list-processing commands; the
list can always be passed to the Tcl interpreter for evaluation).

The Tcl commands `concat`, `foreach`, `lappend`, `lindex`, `linsert`,
`list`, `llength`, `lrange`, `lreplace`, `lsearch`, and `lsort` allow
you to build lists, extract elements from them, search them, and perform
other list-related functions.

Advanced list commands include `lrepeat`, `lreverse`, `lmap`, `lassign`, `lset`.

LIST EXPANSION
--------------

A new addition to Tcl 8.5 is the ability to expand a list into separate
arguments. Support for this feature is also available in Jim.

Consider the following attempt to exec a list:

----
    set cmd {ls -l}
    exec $cmd
----

This will attempt to exec a command named "ls -l", which will clearly not
work. Typically eval and concat are required to solve this problem, however
it can be solved much more easily with +\{*\}+.

----
    exec {*}$cmd
----

This will expand the following argument into individual elements and then evaluate
the resulting command.

Note that the official Tcl syntax is +\{*\}+, however +\{expand\}+ is retained
for backward compatibility with experimental versions of this feature.

REGULAR EXPRESSIONS
-------------------
Jim Tcl provides two commands that support string matching using regular
expressions, `regexp` and `regsub`, as well as `switch -regexp` and
`lsearch -regexp`.

Regular expressions may be implemented one of two ways. Either using the system's C library
POSIX regular expression support, or using the built-in regular expression engine.
The differences between these are described below.

*NOTE* Tcl 7.x and 8.x use perl-style Advanced Regular Expressions (+ARE+).

POSIX Regular Expressions
~~~~~~~~~~~~~~~~~~~~~~~~~
If the system supports POSIX regular expressions, and UTF-8 support is not enabled,
this support will be used by default. The type of regular expressions supported are
Extended Regular Expressions (+ERE+) rather than Basic Regular Expressions (+BRE+).
See REG_EXTENDED in the documentation.

Using the system-supported POSIX regular expressions will typically
make for the smallest code size, but some features such as UTF-8
and +{backslash}w+, +{backslash}d+, +{backslash}s+ are not supported, and null characters
in strings are not supported.

See regex(3) and regex(7) for full details.

Jim built-in Regular Expressions
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The Jim built-in regular expression engine may be selected with +./configure --with-jim-regexp+
or it will be selected automatically if UTF-8 support is enabled.

This engine supports UTF-8 as well as some +ARE+ features. The differences with both Tcl 7.x/8.x
and POSIX are highlighted below.

1. UTF-8 strings and patterns are both supported
2. All Tcl character classes are supported (e.g. +[:alnum:]+, +[:digit:]+, +[:space:]+), but...
3. Character classes apply to ASCII characters only
4. Supported shorthand character classes: +{backslash}w+ = +[:alnum:]+, +{backslash}W+ = +^[:alnum:]+, +{backslash}d+ = +[:digit:],+ +{backslash}D+ = +^[:digit:],+ +{backslash}s+ = +[:space:]+, + +{backslash}S+ = +^[:space:]+
5. Supported constraint escapes: +{backslash}m+ = +{backslash}<+ = start of word, +{backslash}M+ = +{backslash}>+ = end of word, +{backslash}A+ = start of string, +{backslash}Z+ = end of string
6. Backslash escapes may be used within regular expressions, such as +{backslash}n+ = newline, +{backslash}uNNNN+ = unicode
7. Support for the +?+ non-greedy quantifier. e.g. +*?+
8. Support for non-capturing parentheses +(?:...)+
9. Jim Tcl considers that both patterns and strings end at a null character (+\x00+)
10. Jim Tcl does not support back references. e.g. +{backslash}1+

STRING MATCHING
---------------
A number of commands in Jim support C-shell style "glob matching", including
`string match`, `switch -glob`, `array names` and others. This form of string matching
works as follows:

A test occurs where a +'string'+ is matched against a +'pattern'+. The match is considered
successful if the contents of +'string'+ and +'pattern'+ are identical except that the
following special sequences may appear in +'pattern'+:

+*+;;
    Matches any sequence of characters in +'string'+, including an empty string.

+?+;;
    Matches any single character in +'string'+.

+['chars']+;;
    Matches any character in the set given by +'chars'+.
    If a sequence of the form +'x-y'+ appears in +'chars'+,
    then any character between +'x'+ and +'y'+, inclusive,
    will match.

+{backslash}x+;;
    Matches the single character +'x'+.  This provides a way of
    avoiding the special interpretation of the characters +{backslash}*?[]+
    in +'pattern'+.

COMMAND RESULTS
---------------
Each command produces two results:  a code and a string.  The
code indicates whether the command completed successfully or not,
and the string gives additional information.  The valid codes are
defined in jim.h, and are:

+JIM_OK(0)+::
    This is the normal return code, and indicates that the command completed
    successfully.  The string gives the command's return value.

+JIM_ERR(1)+::
    Indicates that an error occurred; the string gives a message describing
    the error.

+JIM_RETURN(2)+::
    Indicates that the `return` command has been invoked, and that the
    current procedure (or top-level command or `source` command)
    should return immediately.  The
    string gives the return value for the procedure or command.

+JIM_BREAK(3)+::
    Indicates that the `break` command has been invoked, so the
    innermost loop should abort immediately.  The string should always
    be empty.

+JIM_CONTINUE(4)+::
    Indicates that the `continue` command has been invoked, so the
    innermost loop should go on to the next iteration.  The string
    should always be empty.

+JIM_SIGNAL(5)+::
    Indicates that a signal was caught while executing a commands.
    The string contains the name of the signal caught.
    See the `signal` and `catch` commands.

+JIM_EXIT(6)+::
    Indicates that the command called the `exit` command.
    The string contains the exit code.

Tcl programmers do not normally need to think about return codes,
since +JIM_OK+ is almost always returned.  If anything else is returned
by a command, then the Tcl interpreter immediately stops processing
commands and returns to its caller.  If there are several nested
invocations of the Tcl interpreter in progress, then each nested
command will usually return the error to its caller, until eventually
the error is reported to the top-level application code.  The
application will then display the error message for the user.

In a few cases, some commands will handle certain `error` conditions
themselves and not return them upwards.  For example, the `for`
command checks for the +JIM_BREAK+ code; if it occurs, then `for`
stops executing the body of the loop and returns +JIM_OK+ to its
caller.  The `for` command also handles +JIM_CONTINUE+ codes and the
procedure interpreter handles +JIM_RETURN+ codes.  The `catch`
command allows Tcl programs to catch errors and handle them without
aborting command interpretation any further.

The `info returncodes` command may be used to programmatically map between
return codes and names.

PROCEDURES
----------
Tcl allows you to extend the command interface by defining
procedures.  A Tcl procedure can be invoked just like any other Tcl
command (it has a name and it receives one or more arguments).
The only difference is that its body isn't a piece of C code linked
into the program; it is a string containing one or more other
Tcl commands.

The `proc` command is used to create a new Tcl command procedure:

+*proc* 'name arglist ?statics? body'+

The new command is named +'name'+, and it replaces any existing command
there may have been by that name. Whenever the new command is
invoked, the contents of +'body'+ will be executed by the Tcl
interpreter.

+'arglist'+ specifies the formal arguments to the procedure.
It consists of a list, possibly empty, of the following
argument specifiers:

+name+::
    Required Argument - A simple argument name.

+{name default}+::
    Optional Argument - A two-element list consisting of the
    argument name, followed by the default value, which will
    be used if the corresponding argument is not supplied.

+&name+::
    Reference Argument - The caller is expected to pass the name of
    an existing variable. An implicit +`upvar` 1 origname name+ is done
    to make the variable available in the proc scope.

+*args*+::
    Variable Argument - The special name +'args'+, which is
    assigned all remaining arguments (including none) as a list. The
    variable argument may only be specified once. Note that
    the syntax +{args newname}+ may be used to retain the special
    behaviour of +'args'+ with a different local name. In this case,
    the variable is named +'newname'+ rather than +'args'+.

When the command is invoked, a local variable will be created for each of
the formal arguments to the procedure; its value will be the value
of corresponding argument in the invoking command or the argument's
default value.

Arguments with default values need not be specified in a procedure
invocation.  However, there must be enough actual arguments for all
required arguments, and there must not be any extra actual arguments
(unless the Variable Argument is specified).

Actual arguments are assigned to formal arguments as in left-to-right
order with the following precedence.

1. Required Arguments (including Reference Arguments)
2. Optional Arguments
3. Variable Argument

The following example illustrates precedence. Assume a procedure declaration:

----
    proc p {{a A} args b {c C} d} {...}
----

This procedure requires at least two arguments, but can accept an unlimited number.
The following table shows how various numbers of arguments are assigned.
Values marked as +-+ are assigned the default value.

[width="40%",frame="topbot",options="header"]
|==============
|Number of arguments|a|args|b|c|d
|2|-|-|1|-|2
|3|1|-|2|-|3
|4|1|-|2|3|4
|5|1|2|3|4|5
|6|1|2,3|4|5|6
|==============

When +'body'+ is being executed, variable names normally refer to local
variables, which are created automatically when referenced and deleted
when the procedure returns.  One local variable is automatically created
for each of the procedure's arguments.  Global variables can be
accessed by invoking the `global` command or via the +::+ prefix.

New in Jim
~~~~~~~~~~
In addition to procedure arguments, Jim procedures may declare static variables.
These variables scoped to the procedure and initialised at procedure definition.
Either from the static variable definition, or from the enclosing scope.

Consider the following example:

----
    . set a 1
    . proc a {} {a {b 2}} {
        set c 1
        puts "$a $b $c"
        incr a
        incr b
        incr c
    }
    . a
    1 2 1
    . a
    2 3 1
----

The static variable +'a'+ has no initialiser, so it is initialised from
the enclosing scope with the value 1. (Note that it is an error if there
is no variable with the same name in the enclosing scope). However +'b'+
has an initialiser, so it is initialised to 2.

Unlike a local variable, the value of a static variable is retained across
invocations of the procedure.

See the `proc` command for information on how to define procedures
and what happens when they are invoked. See also <<_namespaces,NAMESPACES>>.

VARIABLES - SCALARS AND ARRAYS
------------------------------
Tcl allows the definition of variables and the use of their values
either through '$'-style variable substitution, the `set`
command, or a few other mechanisms.

Variables need not be declared:  a new variable will automatically
be created each time a new variable name is used.

Tcl supports two types of variables:  scalars and arrays.
A scalar variable has a single value, whereas an array variable
can have any number of elements, each with a name (called
its 'index') and a value.

Array indexes may be arbitrary strings; they need not be numeric.
Parentheses are used refer to array elements in Tcl commands.
For example, the command

----
    set x(first) 44
----

will modify the element of 'x' whose index is 'first'
so that its new value is '44'.

Two-dimensional arrays can be simulated in Tcl by using indexes
that contain multiple concatenated values.
For example, the commands

----
    set a(2,3) 1
    set a(3,6) 2
----

set the elements of 'a' whose indexes are '2,3' and '3,6'.

In general, array elements may be used anywhere in Tcl that scalar
variables may be used.

If an array is defined with a particular name, then there may
not be a scalar variable with the same name.

Similarly, if there is a scalar variable with a particular
name then it is not possible to make array references to the
variable.

To convert a scalar variable to an array or vice versa, remove
the existing variable with the `unset` command.

The `array` command provides several features for dealing
with arrays, such as querying the names of all the elements of
the array and converting between an array and a list.

Variables may be either global or local.  If a variable
name is used when a procedure isn't being executed, then it
automatically refers to a global variable.  Variable names used
within a procedure normally refer to local variables associated with that
invocation of the procedure.  Local variables are deleted whenever
a procedure exits.  Either `global` command may be used to request
that a name refer to a global variable for the duration of the current
procedure (this is somewhat analogous to 'extern' in C), or the variable
may be explicitly scoped with the +::+ prefix. For example

----
    . set a 1
    . set b 2
    . proc p {} {
        set c 3
        global a

        puts "$a $::b $c"
    }
    . p
----

will output:

    1 2 3

ARRAYS AS LISTS IN JIM
----------------------
Unlike Tcl, Jim can automatically convert between a list (with an even
number of elements) and an array value. This is similar to the way Tcl
can convert between a string and a list.

For example:

----
  set a {1 one 2 two}
  puts $a(2)
----

will output:

----
  two
----

Thus `array set` is equivalent to `set` when the variable does not
exist or is empty.

The reverse is also true where an array will be converted into
a list.

----
  set a(1) one; set a(2) two
  puts $a
----

will output:

----
  1 one 2 two
----

DICTIONARY VALUES
-----------------
Tcl 8.5 introduced the dict command, and Jim Tcl has added a version
of this command. Dictionaries provide efficient access to key-value
pairs, just like arrays, but dictionaries are pure values. This
means that you can pass them to a procedure just as a list or a
string. Tcl dictionaries are therefore much more like Tcl lists,
except that they represent a mapping from keys to values, rather
than an ordered sequence.

You can nest dictionaries, so that the value for a particular key
consists of another dictionary. That way you can elegantly build
complicated data structures, such as hierarchical databases. You
can also combine dictionaries with other Tcl data structures. For
instance, you can build a list of dictionaries that themselves
contain lists.

Dictionaries are values that contain an efficient, order-preserving
mapping from arbitrary keys to arbitrary values. Each key in the
dictionary maps to a single value. They have a textual format that
is exactly that of any list with an even number of elements, with
each mapping in the dictionary being represented as two items in
the list. When a command takes a dictionary and produces a new
dictionary based on it (either returning it or writing it back into
the variable that the starting dictionary was read from) the new
dictionary will have the same order of keys, modulo any deleted
keys and with new keys added on to the end. When a string is
interpreted as a dictionary and it would otherwise have duplicate
keys, only the last value for a particular key is used; the others
are ignored, meaning that, "apple banana" and "apple carrot apple
banana" are equivalent dictionaries (with different string
representations).

Note that in Jim, arrays are implemented as dictionaries.
Thus automatic conversion between lists and dictionaries applies
as it does for arrays.

----
  . dict set a 1 one
  1 one
  . dict set a 2 two
  1 one 2 two
  . puts $a
  1 one 2 two
  . puts $a(2)
  two
  . dict set a 3 T three
  1 one 2 two 3 {T three}
----

See the `dict` command for more details.

NAMESPACES
----------
Tcl added namespaces as a mechanism avoiding name clashes, especially in applications
including a number of 3rd party components. While there is less need for namespaces
in Jim Tcl (which does not strive to support large applications), it is convenient to
provide a subset of the support for namespaces to easy porting code from Tcl.

Jim Tcl currently supports "light-weight" namespaces which should be adequate for most
purposes. This feature is currently experimental. See README.namespaces for more information
and the documentation of the `namespace` command.

GARBAGE COLLECTION, REFERENCES, LAMBDA FUNCTION
-----------------------------------------------
Unlike Tcl, Jim has some sophisticated support for functional programming.
These are described briefly below.

More information may be found at http://wiki.tcl.tk/13847

References
~~~~~~~~~~
A reference can be thought of as holding a value with one level of indirection,
where the value may be garbage collected when unreferenced.
Consider the following example:

----
    . set r [ref "One String" test]
    <reference.<test___>.00000000000000000000>
    . getref $r
    One String
----

The operation `ref` creates a references to the value specified by the
first argument. (The second argument is a "type" used for documentation purposes).

The operation `getref` is the dereferencing operation which retrieves the value
stored in the reference.

----
    . setref $r "New String"
    New String
    . getref $r
    New String
----

The operation `setref` replaces the value stored by the reference. If the old value
is no longer accessible by any reference, it will eventually be automatically be garbage
collected.

Garbage Collection
~~~~~~~~~~~~~~~~~~
Normally, all values in Tcl are passed by value. As such values are copied and released
automatically as necessary.

With the introduction of references, it is possible to create values whose lifetime
transcend their scope. To support this, case, the Jim system will periodically identify
and discard objects which are no longer accessible by any reference.

The `collect` command may be used to force garbage collection.  Consider a reference created
with a finalizer:

----
    . proc f {ref value} { puts "Finaliser called for $ref,$value" }
    . set r [ref "One String" test f]
    <reference.<test___>.00000000000
    . collect
    0
    . set r ""
    . collect
    Finaliser called for <reference.<test___>.00000000000,One String
    1
----

Note that once the reference, 'r', was modified so that it no longer
contained a reference to the value, the garbage collector discarded
the value (after calling the finalizer).

The finalizer for a reference may be examined or changed with the `finalize` command

----
    . finalize $r
    f
    . finalize $r newf
    newf
----

Lambda Function
~~~~~~~~~~~~~~~
Jim provides a garbage collected `lambda` function. This is a procedure
which is able to create an anonymous procedure.  Consider:

----
    . set f [lambda {a} {{x 0}} { incr x $a }]
    . $f 1
    1
    . $f 2
    3
    . set f ""
----

This create an anonymous procedure (with the name stored in 'f'), with a static variable
which is incremented by the supplied value and the result returned.

Once the procedure name is no longer accessible, it will automatically be deleted
when the garbage collector runs.

The procedure may also be delete immediately by renaming it "". e.g.

----
    . rename $f ""
----

UTF-8 AND UNICODE
-----------------
If Jim is built with UTF-8 support enabled (configure --enable-utf),
then most string-related commands become UTF-8 aware.  These include,
but are not limited to, `string match`, `split`, `glob`, `scan` and
`format`.

UTF-8 encoding has many advantages, but one of the complications is that
characters can take a variable number of bytes. Thus the addition of
`string bytelength` which returns the number of bytes in a string,
while `string length` returns the number of characters.

If UTF-8 support is not enabled, all commands treat bytes as characters
and `string bytelength` returns the same value as `string length`.

Note that even if UTF-8 support is not enabled, the +{backslash}uNNNN+ and related syntax
is still available to embed UTF-8 sequences.

Jim Tcl supports all currently defined unicode codepoints. That is 21 bits, up to +'U+1FFFFF'.

String Matching
~~~~~~~~~~~~~~~
Commands such as `string match`, `lsearch -glob`, `array names` and others use
<<_string_matching,STRING MATCHING>> rules. These commands support UTF-8. For example:

----
  string match a\[\ua0-\ubf\]b "a\u00a3b"
----

format and scan
~~~~~~~~~~~~~~~
+format %c+ allows a unicode codepoint to be be encoded. For example, the following will return
a string with two bytes and one character. The same as +{backslash}ub5+

----
  format %c 0xb5
----

`format` respects widths as character widths, not byte widths. For example, the following will
return a string with three characters, not three bytes.

----
  format %.3s \ub5\ub6\ub7\ub8
----

Similarly, +scan ... %c+ allows a UTF-8 to be decoded to a unicode codepoint. The following will set
+'a'+ to 181 (0xb5) and +'b'+ to 65 (0x41).

----
  scan \u00b5A %c%c a b
----

`scan %s` will also accept a character class, including unicode ranges.

String Classes
~~~~~~~~~~~~~~
`string is` has *not* been extended to classify UTF-8 characters. Therefore, the following
will return 0, even though the string may be considered to be alphabetic.

----
  string is alpha \ub5Test
----

This does not affect the string classes 'ascii', 'control', 'digit', 'double', 'integer' or 'xdigit'.

Case Mapping and Conversion
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jim provides a simplified unicode case mapping. This means that case conversion
and comparison will not increase or decrease the number of characters in a string.
(Although it may change the number of bytes).

`string toupper` will convert any lowercase letters to their uppercase equivalent.
Any character which is not a letter or has no uppercase equivalent is left unchanged.
Similarly for `string tolower` and `string totitle`.

Commands which perform case insensitive matches, such as `string compare -nocase`
and `lsearch -nocase` fold both strings to uppercase before comparison.

Invalid UTF-8 Sequences
~~~~~~~~~~~~~~~~~~~~~~~
Some UTF-8 character sequences are invalid, such as those beginning with '0xff',
those which represent character sequences longer than 3 bytes (greater than U+FFFF),
and those which end prematurely, such as a lone '0xc2'.

In these situations, the offending bytes are treated as single characters. For example,
the following returns 2.

----
  string bytelength \xff\xff
----

Regular Expressions
~~~~~~~~~~~~~~~~~~~
If UTF-8 support is enabled, the built-in regular expression engine will be
selected which supports UTF-8 strings and patterns.

See <<_regular_expressions,REGULAR EXPRESSIONS>>

BUILT-IN COMMANDS
-----------------
The Tcl library provides the following built-in commands, which will
be available in any application using Tcl.  In addition to these
built-in commands, there may be additional commands defined by each
application, plus commands defined as Tcl procedures.

In the command syntax descriptions below, words in +*boldface*+ are
literals that you type verbatim to Tcl.

Words in +'italics'+ are meta-symbols; they serve as names for any of
a range of values that you can type.

Optional arguments or groups of arguments are indicated by enclosing them
in +?question-marks?+.

Ellipses (+\...+) indicate that any number of additional
arguments or groups of arguments may appear, in the same format
as the preceding argument(s).

[[CommandIndex]]
Command Index
~~~~~~~~~~~~~
@INSERTINDEX@

alarm
~~~~~
+*alarm* 'seconds'+

Delivers the +SIGALRM+ signal to the process after the given
number of seconds. If the platform supports 'ualarm(3)' then
the argument may be a floating point value. Otherwise it must
be an integer.

Note that unless a signal handler for +SIGALRM+ has been installed
(see `signal`), the process will exit on this signal.

alias
~~~~~
+*alias* 'name args\...'+

Creates a single word alias (command) for one or more words. For example,
the following creates an alias for the command `info exists`.

----
    alias e info exists
    if {[e var]} {
      ...
    }
----

`alias` returns +'name'+, allowing it to be used with `local`.

See also `proc`, `curry`, `lambda`, `local`, `info alias`, `exists -alias`

append
~~~~~~
+*append* 'varName value ?value value ...?'+

Append all of the +'value'+ arguments to the current value
of variable +'varName'+.  If +'varName'+ doesn't exist,
it is given a value equal to the concatenation of all the
+'value'+ arguments.

This command provides an efficient way to build up long
variables incrementally.
For example, "`append a $b`" is much more efficient than
"`set a $a$b`" if +$a+ is long.

apply
~~~~~~
+*apply* 'lambdaExpr ?arg1 arg2 \...?'+

The command `apply` provides for anonymous procedure calls,
similar to `lambda`, but without a command name being created, even temporarily.

The function  +'lambdaExpr'+ is a two element list, +{args body}+
or a three element list, +{args body namespace}+. The first element
+'args'+ specifies the formal arguments in the same form as the `proc` and `lambda` commands.

array
~~~~~
+*array* 'option arrayName ?arg\...?'+

This command performs one of several operations on the
variable given by +'arrayName'+.

Note that in general, if the named array does not exist, the +'array'+ command behaves
as though the array exists but is empty.

The +'option'+ argument determines what action is carried out by the
command.  The legal +'options'+ (which may be abbreviated) are:

+*array exists* 'arrayName'+::
    Returns 1 if +'arrayName'+ is an array variable, 0 if there is
    no variable by that name.

+*array get* 'arrayName ?pattern?'+::
    Returns a list containing pairs of elements. The first
    element in each pair is the name of an element in +'arrayName'+
    and the second element of each pair is the value of the
    array element. The order of the pairs is undefined. If
    +'pattern'+ is not specified, then all of the elements of the
    array are included in the result. If +'pattern'+ is specified,
    then only those elements whose names match +'pattern'+ (using
    <<_string_matching,STRING MATCHING>> rules) are included. If +'arrayName'+
    isn't the name of an array variable, or if the array contains
    no elements, then an empty list is returned.

+*array names* 'arrayName ?pattern?'+::
    Returns a list containing the names of all of the elements
    in the array that match +'pattern'+. If +'pattern'+ is omitted then
    the command returns all of the element names in the array.
    If +'pattern'+ is specified, then only those elements whose
    names match +'pattern'+ (using <<_string_matching,STRING MATCHING>> rules)
    are included. If there are no (matching) elements
    in the array, or if +'arrayName'+ isn't the name of an array
    variable, then an empty string is returned.

+*array set* 'arrayName list'+::
    Sets the values of one or more elements in +'arrayName'+. +'list'+
    must have a form like that returned by array get, consisting
    of an even number of elements. Each odd-numbered element
    in list is treated as an element name within arrayName, and
    the following element in list is used as a new value for
    that array element. If the variable +'arrayName'+ does not
    already exist and list is empty, +'arrayName'+ is created with
    an empty array value.

+*array size* 'arrayName'+::
    Returns the number of elements in the array. If +'arrayName'+
    isn't the name of an array then 0 is returned.

+*array unset* 'arrayName ?pattern?'+::
    Unsets all of the elements in the array that match +'pattern'+
    (using <<_string_matching,STRING MATCHING>> rules). If +'arrayName'+
    isn't the name of an array variable or there are no matching
    elements in the array, no error will be raised. If +'pattern'+
    is omitted and +'arrayName'+ is an array variable, then the
    command unsets the entire array. The command always returns
    an empty string.

break
~~~~~
+*break*+

This command may be invoked only inside the body of a loop command
such as `for` or `foreach` or `while`.  It returns a +JIM_BREAK+ code
to signal the innermost containing loop command to return immediately.

case
~~~~
The obsolete '+*case*+' command has been removed from Jim Tcl since v0.75.
Use `switch` instead.

catch
~~~~~
+*catch* ?-?no?'code \...'? ?--? 'command ?resultVarName? ?optionsVarName?'+

The `catch` command may be used to prevent errors from aborting
command interpretation.  `catch` evaluates +'command'+, and returns a
+JIM_OK+ code, regardless of any errors that might occur while
executing +'command'+ (with the possible exception of +JIM_SIGNAL+ -
see below).

The return value from `catch` is a decimal string giving the code
returned by the Tcl interpreter after executing +'command'+.  This
will be '0' (+JIM_OK+) if there were no errors in +'command'+; otherwise
it will have a non-zero value corresponding to one of the exceptional
return codes (see jim.h for the definitions of code values, or the
`info returncodes` command).

If the +'resultVarName'+ argument is given, then it gives the name
of a variable; `catch` will set the value of the variable to the
string returned from +'command'+ (either a result or an error message).

If the +'optionsVarName'+ argument is given, then it gives the name
of a variable; `catch` will set the value of the variable to a
dictionary. For any return code other than +JIM_RETURN+, the value
for the key +-code+ will be set to the return code. For +JIM_RETURN+
it will be set to the code given in `return -code`. Additionally,
for the return code +JIM_ERR+, the value of the key +-errorinfo+
will contain the current stack trace (the same result as `info stacktrace`),
the value of the key +-errorcode+ will contain the
same value as the global variable $::errorCode, and the value of
the key +-level+ will be the current return level (see `return -level`).
This can be useful to rethrow an error:

----
    if {[catch {...} msg opts]} {
        ...maybe do something with the error...
        incr opts(-level)
        return {*}$opts $msg
    }
----

Normally `catch` will +'not'+ catch any of the codes +JIM_EXIT+, +JIM_EVAL+ or +JIM_SIGNAL+.
The set of codes which will be caught may be modified by specifying the one more codes before
+'command'+.

e.g. To catch +JIM_EXIT+ but not +JIM_BREAK+ or +JIM_CONTINUE+

----
    catch -exit -nobreak -nocontinue -- { ... }
----

The use of +--+ is optional. It signifies that no more return code options follow.

Note that if a signal marked as `signal handle` is caught with `catch -signal`, the return value
(stored in +'resultVarName'+) is name of the signal caught.

cd
~~
+*cd* 'dirName'+

Change the current working directory to +'dirName'+.

Returns an empty string.

This command can potentially be disruptive to an application, so it may
be removed in some applications.

clock
~~~~~
+*clock seconds*+::
    Returns the current time as seconds since the epoch.

+*clock clicks*+::
    Returns the current time in "clicks", a system-dependent, high-resolution time.

+*clock microseconds*+::
    Returns the current time in microseconds.

+*clock milliseconds*+::
    Returns the current time in milliseconds.

+*clock format* 'seconds' ?*-format* 'format?' ?*-gmt* 'boolean?'+::
    Format the given time (seconds since the epoch) according to the given
    format. See strftime(3) for supported formats.
    If no format is supplied, "%c" is used.
  ::
    If +'boolean'+ is true, processing is performed in UTC.
    If +'boolean'+ is false (the default), processing  is performed in the local time zone.

+*clock scan* 'str' *-format* 'format' ?*-gmt* 'boolean?'+::
    Scan the given time string using the given format string.
    See strptime(3) for supported formats.
    See `clock format` for the handling of '-gmt'.

*NOTE* Some systems such as 32-bit Linux have only a 32-bit time_t, and are therefore not year 2038
compliant.

close
~~~~~
+*close* 'fileId'+

+'fileId' *close*+

Closes the file given by +'fileId'+.
+'fileId'+ must be the return value from a previous invocation
of the `open` command; after this command, it should not be
used anymore.

collect
~~~~~~~
+*collect*+

Normally reference garbage collection is automatically performed periodically.
However it may be run immediately with the `collect` command.

See <<_garbage_collection_references_lambda_function,GARBAGE COLLECTION>> for more detail.

concat
~~~~~~
+*concat* 'arg ?arg \...?'+

This command treats each argument as a list and concatenates them
into a single list.  It permits any number of arguments.  For example,
the command

----
    concat a b {c d e} {f {g h}}
----

will return

----
    a b c d e f {g h}
----

as its result.

continue
~~~~~~~~
+*continue*+

This command may be invoked only inside the body of a loop command such
as `for` or `foreach` or `while`.  It returns a  +JIM_CONTINUE+ code to
signal the innermost containing loop command to skip the remainder of
the loop's body but continue with the next iteration of the loop.

curry
~~~~~
+*alias* 'args\...'+

Similar to `alias` except it creates an anonymous procedure (lambda) instead of
a named procedure.

the following creates a local, unnamed alias for the command `info exists`.

----
    set e [local curry info exists]
    if {[$e var]} {
      ...
    }
----

`curry` returns the name of the procedure.

See also `proc`, `alias`, `lambda`, `local`.

dict
~~~~
+*dict* 'option ?arg\...?'+

Performs one of several operations on dictionary values.

The +'option'+ argument determines what action is carried out by the
command.  The legal +'options'+ are:

+*dict create* '?key value \...?'+::
    Create and return a new dictionary value that contains each of
    the key/value mappings listed as  arguments (keys and values
    alternating, with each key being followed by its associated
    value.)

+*dict exists* 'dictionary key ?key \...?'+::
    Returns a boolean value indicating whether the given key (or path
    of keys through a set of nested dictionaries) exists in the given
    dictionary value.  This returns a true value exactly when `dict get`
    on that path will succeed.

+*dict get* 'dictionary ?key \...?'+::
    Given a dictionary value (first argument) and a key (second argument),
    this will retrieve the value for that key. Where several keys are
    supplied, the behaviour of the command shall be as if the result
    of "`dict get $dictVal $key`" was passed as the first argument to
    dict get with the remaining arguments as second (and possibly
    subsequent) arguments. This facilitates lookups in nested dictionaries.
    If no keys are provided, dict would return a list containing pairs
    of elements in a manner similar to array get. That is, the first
    element of each pair would be the key and the second element would
    be the value for that key.  It is an error to attempt to retrieve
    a value for a key that is not present in the dictionary.

+*dict getdef* 'dictionary ?key \...? key default'+::
    Alias for `dict getwithdefault`.

+*dict getwithdefault* 'dictionary ?key \...? key default'+::
    Similar to `dict get` except if no value exists in the dictionary for the
    give key(s), returns +'default'+ instead.

+*dict keys* 'dictionary ?pattern?'+::
    Returns a list of the keys in the dictionary.
    If +'pattern'+ is specified, then only those keys whose
    names match +'pattern'+ (using <<_string_matching,STRING MATCHING>> rules)
    are included.

+*dict merge* ?'dictionary \...'?+::
    Return a dictionary that contains the contents of each of the
    +'dictionary'+ arguments. Where two (or more) dictionaries
    contain a mapping for the same key, the resulting dictionary
    maps that key to the value according to the last dictionary on
    the command line containing a mapping for that key.

+*dict set* 'dictionaryName key ?key \...? value'+::
    This operation takes the +'name'+ of a variable containing a dictionary
    value and places an updated dictionary value in that variable
    containing a mapping from the given key to the given value. When
    multiple keys are present, this operation creates or updates a chain
    of nested dictionaries.

+*dict size* 'dictionary'+::
    Return the number of key/value mappings in the given dictionary value.

+*dict unset* 'dictionaryName key ?key \...? value'+::
    This operation (the companion to `dict set`) takes the name of a
    variable containing a dictionary value and places an updated
    dictionary value in that variable that does not contain a mapping
    for the given key. Where multiple keys are present, this describes
    a path through nested dictionaries to the mapping to remove. At
    least one key must be specified, but the last key on the key-path
    need not exist. All other components on the path must exist.

+*dict with* 'dictionaryName key ?key \...? script'+::
    Execute the Tcl script in +'script'+ with the value for each
    key in +'dictionaryName'+ mapped to a variable with the same
    name. Where one or more keys are given, these indicate a chain
    of nested dictionaries, with the innermost dictionary being the
    one opened out for the execution of body. Making +'dictionaryName'+
    unreadable will make the updates to the dictionary be discarded,
    and this also happens if the contents of +'dictionaryName'+ are
    adjusted so that the chain of dictionaries no longer exists.
    The result of `dict with` is (unless some kind of error occurs)
    the result of the evaluation of body.
 ::
    The variables are mapped in the scope enclosing the `dict with`;
    it is recommended that this command only be used in a local
    scope (procedure). Because of this, the variables set by
    `dict with` will continue to exist after the command finishes (unless
    explicitly unset). Note that changes to the contents of +'dictionaryName'+
    only happen when +'script'+ terminates.

+*dict for, values, incr, append, lappend, update, info, replace*+ to be documented...

env
~~~
+*env* '?name? ?default?'+

If +'name'+ is supplied, returns the value of +'name'+ from the initial
environment (see getenv(3)). An error is returned if +'name'+ does not
exist in the environment, unless +'default'+ is supplied - in which case
that value is returned instead.

If no arguments are supplied, returns a list of all environment variables
and their values as +{name value \...}+

See also the global variable +::env+

eof
~~~
+*eof* 'fileId'+

+'fileId' *eof*+

Returns 1 if an end-of-file condition has occurred on +'fileId'+,
0 otherwise.

+'fileId'+ must have been the return value from a previous call to `open`,
or it may be +stdin+, +stdout+, or +stderr+ to refer to one of the
standard I/O channels.

error
~~~~~
+*error* 'message ?stacktrace?'+

Returns a +JIM_ERR+ code, which causes command interpretation to be
unwound.  +'message'+ is a string that is returned to the application
to indicate what went wrong.

If the +'stacktrace'+ argument is provided and is non-empty,
it is used to initialize the stacktrace.

This feature is most useful in conjunction with the `catch` command:
if a caught error cannot be handled successfully, +'stacktrace'+ can be used
to return a stack trace reflecting the original point of occurrence
of the error:

----
    catch {...} errMsg
    ...
    error $errMsg [info stacktrace]
----

See also `errorInfo`, `info stacktrace`, `catch` and `return`

errorInfo
~~~~~~~~~
+*errorInfo* 'error ?stacktrace?'+

Returns a human-readable representation of the given error message and stack trace.
Typical usage is:

----
    if {[catch {...} error]} {
        puts stderr [errorInfo $error [info stacktrace]]
        exit 1
    }
----

See also `error`.

eval
~~~~
+*eval* 'arg ?arg\...?'+

`eval` takes one or more arguments, which together comprise a Tcl
command (or collection of Tcl commands separated by newlines in the
usual way).  `eval` concatenates all its arguments in the same
fashion as the `concat` command, passes the concatenated string to the
Tcl interpreter recursively, and returns the result of that
evaluation (or any error generated by it).

exec
~~~~
+*exec* 'arg ?arg\...?'+

This command treats its arguments as the specification
of one or more UNIX commands to execute as subprocesses.
The commands take the form of a standard shell pipeline;
+|+ arguments separate commands in the
pipeline and cause standard output of the preceding command
to be piped into standard input of the next command (or +|&+ for
both standard output and standard error).

Under normal conditions the result of the `exec` command
consists of the standard output produced by the last command
in the pipeline followed by the standard error output.

If any of the commands writes to its standard error file,
then this will be included in the result after the standard output
of the last command.

Note that unlike Tcl, data written to standard error does not cause
`exec` to return an error.

If any of the commands in the pipeline exit abnormally or
are killed or suspended, then `exec` will return an error.
If no standard error output was produced, or is redirected,
the error message will include the normal result, as above,
followed by error messages describing the abnormal terminations.

If any standard error output was produced, these abnormal termination
messages are suppressed.

If the last character of the result or error message
is a newline then that character is deleted from the result
or error message for consistency with normal
Tcl return values.

An +'arg'+ may have one of the following special forms:

+>filename+::
    The standard output of the last command in the pipeline
    is redirected to the file.  In this situation `exec`
    will normally return an empty string.

+>>filename+::
    As above, but append to the file.

+>@fileId+::
    The standard output of the last command in the pipeline is
    redirected to the given (writable) file descriptor (e.g. stdout,
    stderr, or the result of `open`). In this situation `exec`
    will normally return an empty string.

+2>filename+::
    The standard error of the last command in the pipeline
    is redirected to the file.

+2>>filename+::
    As above, but append to the file.

+2>@fileId+::
    The standard error of the last command in the pipeline is
    redirected to the given (writable) file descriptor.

+2>@1+::
    The standard error of the last command in the pipeline is
    redirected to the same file descriptor as the standard output.

+>&filename+::
    Both the standard output and standard error of the last command
    in the pipeline is redirected to the file.

+>>&filename+::
    As above, but append to the file.

+<filename+::
    The standard input of the first command in the pipeline
    is taken from the file.

+<<string+::
    The standard input of the first command is taken as the
    given immediate value.

+<@fileId+::
    The standard input of the first command in the pipeline
    is taken from the given (readable) file descriptor.

If there is no redirection of standard input, standard error
or standard output, these are connected to the corresponding
input or output of the application.

If the last +'arg'+ is +&+ then the command will be
executed in background.
In this case the standard output from the last command
in the pipeline will
go to the application's standard output unless
redirected in the command, and error output from all
the commands in the pipeline will go to the application's
standard error file. The return value of exec in this case
is a list of process ids (pids) in the pipeline.

Each +'arg'+ becomes one word for a command, except for
+|+, +<+, +<<+, +>+, and +&+ arguments, and the
arguments that follow +<+, +<<+, and +>+.

The first word in each command is taken as the command name;
the directories in the PATH environment variable are searched for
an executable by the given name.

No `glob` expansion or other shell-like substitutions
are performed on the arguments to commands.

If the command fails, the global $::errorCode (and the -errorcode
option in `catch`) will be set to a list, as follows:

+*CHILDKILLED* 'pid sigName msg'+::
        This format is used when a child process has been killed
        because of a signal. The pid element will be the process's
        identifier (in decimal). The sigName element will be the
        symbolic name of the signal that caused the process to
        terminate; it will be one of the names from the include
        file signal.h, such as SIGPIPE. The msg element will be a
        short human-readable message describing the signal, such
        as "write on pipe with no readers" for SIGPIPE.

+*CHILDSUSP* 'pid sigName msg'+::
        This format is used when a child process has been suspended
        because of a signal. The pid element will be the process's
        identifier, in decimal. The sigName element will be the
        symbolic name of the signal that caused the process to
        suspend; this will be one of the names from the include
        file signal.h, such as SIGTTIN. The msg element will be a
        short human-readable message describing the signal, such
        as "background tty read" for SIGTTIN.

+*CHILDSTATUS* 'pid code'+::
        This format is used when a child process has exited with a
        non-zero exit status. The pid element will be the process's
        identifier (in decimal) and the code element will be the
        exit code returned by the process (also in decimal).

The environment for the executed command is set from $::env (unless
this variable is unset, in which case the original environment is used).

exists
~~~~~~
+*exists ?-var|-proc|-command|-alias?* 'name'+

Checks the existence of the given variable, procedure, command
or alias respectively and returns 1 if it exists or 0 if not.  This command
provides a more simplified/convenient version of `info exists`,
`info procs` and `info commands`.

If the type is omitted, a type of '-var' is used. The type may be abbreviated.

exit
~~~~
+*exit* '?returnCode?'+

Terminate the process, returning +'returnCode'+ to the
parent as the exit status.

If +'returnCode'+ isn't specified then it defaults
to 0.

Note that exit can be caught with `catch`.

expr
~~~~
+*expr* 'arg'+

Calls the expression processor to evaluate +'arg'+, and returns
the result as a string.  See the section <<_expressions,EXPRESSIONS>> above.

Note that Jim supports a shorthand syntax for `expr` as +$(\...)+
The following two are identical.

----
  set x [expr {3 * 2 + 1}]
  set x $(3 * 2 + 1)
----

file
~~~~
+*file* 'option name ?arg\...?'+

Operate on a file or a file name.  +'name'+ is the name of a file.

+'option'+ indicates what to do with the file name.  Any unique
abbreviation for +'option'+ is acceptable.  The valid options are:

+*file atime* 'name'+::
    Return a decimal string giving the time at which file +'name'+
    was last accessed.  The time is measured in the standard UNIX
    fashion as seconds from a fixed starting time (often January 1, 1970).
    If the file doesn't exist or its access time cannot be queried then an
    error is generated.

+*file copy ?-force?* 'source target'+::
    Copies file +'source'+ to file +'target'+. The source file must exist.
    The target file must not exist, unless +-force+ is specified.

+*file delete ?-force? ?--?* 'name\...'+::
    Deletes file or directory +'name'+. If the file or directory doesn't exist, nothing happens.
    If it can't be deleted, an error is generated. Non-empty directories will not be deleted
    unless the +-force+ options is given. In this case no errors will be generated, even
    if the file/directory can't be deleted. Use +'--'+ if there is any possibility of
    the first name being +'-force'+.

+*file dirname* 'name'+::
    Return all of the characters in +'name'+ up to but not including
    the last slash character.  If there are no slashes in +'name'+
    then return +.+ (a single dot).  If the last slash in +'name'+ is its first
    character, then return +/+.

+*file executable* 'name'+::
    Return '1' if file +'name'+ is executable by
    the current user, '0' otherwise.

+*file exists* 'name'+::
    Return '1' if file +'name'+ exists and the current user has
    search privileges for the directories leading to it, '0' otherwise.

+*file extension* 'name'+::
    Return all of the characters in +'name'+ after and including the
    last dot in +'name'+.  If there is no dot in +'name'+ then return
    the empty string.

+*file isdirectory* 'name'+::
    Return '1' if file +'name'+ is a directory,
    '0' otherwise.

+*file isfile* 'name'+::
    Return '1' if file +'name'+ is a regular file,
    '0' otherwise.

+*file join* 'arg\...'+::
    Joins multiple path components. Note that if any components is
    an absolute path, the preceding components are ignored.
    Thus +"`file` join /tmp /root"+ returns +"/root"+.

+*file link* ?*-hard|-symbolic*? 'newname target'+::
    Creates a hard link (default) or symbolic link from +'newname'+ to +'target'+.
    Note that the sense of this command is the opposite of `file rename` and `file copy`
    and also of `ln`, but this is compatible with Tcl.
    An error is returned if +'target'+ doesn't exist or +'newname'+ already exists.

+*file lstat* 'name varName'+::
    Same as 'stat' option (see below) except uses the +'lstat'+
    kernel call instead of +'stat'+.  This means that if +'name'+
    refers to a symbolic link the information returned in +'varName'+
    is for the link rather than the file it refers to.  On systems that
    don't support symbolic links this option behaves exactly the same
    as the 'stat' option.

+*file mkdir* 'dir1 ?dir2\...?'+::
    Creates each directory specified. For each pathname +'dir'+ specified,
    this command will create all non-existing parent directories
    as well as +'dir'+ itself. If an existing directory is specified,
    then no action is taken and no error is returned. Trying to
    overwrite an existing file with a directory will result in an
    error.  Arguments are processed in the order specified, halting
    at the first error, if any.

+*file mtime* 'name ?time?'+::
    Return a decimal string giving the time at which file +'name'+
    was last modified.  The time is measured in the standard UNIX
    fashion as seconds from a fixed starting time (often January 1, 1970).
    If the file doesn't exist or its modified time cannot be queried then an
    error is generated. If +'time'+ is given, sets the modification time
    of the file to the given value.

+*file mtimeus* 'name ?time_us?'+::
    As for `file mtime` except the time value is in microseconds
    since the epoch (see also `clock microseconds`).
    Note that some platforms and some filesystems don't support high
    resolution timestamps for files.

+*file normalize* 'name'+::
    Return the normalized path of +'name'+. See 'realpath(3)'.

+*file owned* 'name'+::
    Return '1' if file +'name'+ is owned by the current user,
    '0' otherwise.

+*file readable* 'name'+::
    Return '1' if file +'name'+ is readable by
    the current user, '0' otherwise.

+*file readlink* 'name'+::
    Returns the value of the symbolic link given by +'name'+ (i.e. the
    name of the file it points to).  If
    +'name'+ isn't a symbolic link or its value cannot be read, then
    an error is returned.  On systems that don't support symbolic links
    this option is undefined.

+*file rename* ?*-force*? 'oldname' 'newname'+::
    Renames the file from the old name to the new name.
    If +'newname'+ already exists, an error is returned unless +'-force'+ is
    specified.

+*file rootname* 'name'+::
    Return all of the characters in +'name'+ up to but not including
    the last '.' character in the name.  If +'name'+ doesn't contain
    a dot, then return +'name'+.

+*file split* 'name'+::
    Returns a list whose elements are the path components in +'name'+.
    The first element of the list will have the same path type as
    +'name'+. All other elements will be relative. Path separators
    will be discarded.

+*file stat* 'name ?varName?'+::
    Invoke the 'stat' kernel call on +'name'+, and return the result
    as a dictionary with the following keys: 'atime',
    'ctime', 'dev', 'gid', 'ino', 'mode', 'mtime',
    'nlink', 'size', 'type', 'uid', 'mtimeus' (if supported - see `file mtimeus`)
    Each element except 'type' is a decimal string with the value of
    the corresponding field from the 'stat' return structure; see the
    manual entry for 'stat' for details on the meanings of the values.
    The 'type' element gives the type of the file in the same form
    returned by the command `file type`.
    If +'varName'+ is specified, it is taken to be the name of an array
    variable and the values are also stored into the array.

+*file tail* 'name'+::
    Return all of the characters in +'name'+ after the last slash.
    If +'name'+ contains no slashes then return +'name'+.

+*file tempfile* '?template?'+::
    Creates and returns the name of a unique temporary file. If +'template'+ is omitted, a
    default template will be used to place the file in /tmp. See 'mkstemp(3)' for
    the format of the template and security concerns.

+*file type* 'name'+::
    Returns a string giving the type of file +'name'+, which will be
    one of +file+, +directory+, +characterSpecial+,
    +blockSpecial+, +fifo+, +link+, or +socket+.

+*file writable* 'name'+::
    Return '1' if file +'name'+ is writable by
    the current user, '0' otherwise.

The `file` commands that return 0/1 results are often used in
conditional or looping commands, for example:

----
    if {![file exists foo]} {
        error {bad file name}
    } else {
        ...
    }
----

finalize
~~~~~~~~
+*finalize* 'reference ?command?'+

If +'command'+ is omitted, returns the finalizer command for the given reference.

Otherwise, sets a new finalizer command for the given reference. +'command'+ may be
the empty string to remove the current finalizer.

The reference must be a valid reference create with the `ref`
command.

See <<_garbage_collection_references_lambda_function,GARBAGE COLLECTION>> for more detail.

flush
~~~~~
+*flush* 'fileId'+

+'fileId' *flush*+

Flushes any output that has been buffered for +'fileId'+.  +'fileId'+ must
have been the return value from a previous call to `open`, or it may be
+stdout+ or +stderr+ to access one of the standard I/O streams; it must
refer to a file that was opened for writing.  This command returns an
empty string.

for
~~~
+*for* 'start test next body'+

`for` is a looping command, similar in structure to the C `for` statement.
The +'start'+, +'next'+, and +'body'+ arguments must be Tcl command strings,
and +'test'+ is an expression string.

The `for` command first invokes the Tcl interpreter to execute +'start'+.
Then it repeatedly evaluates +'test'+ as an expression; if the result is
non-zero it invokes the Tcl interpreter on +'body'+, then invokes the Tcl
interpreter on +'next'+, then repeats the loop.  The command terminates
when +'test'+ evaluates to 0.

If a `continue` command is invoked within +'body'+ then any remaining
commands in the current execution of +'body'+ are skipped; processing
continues by invoking the Tcl interpreter on +'next'+, then evaluating
+'test'+, and so on.

If a `break` command is invoked within +'body'+ or +'next'+, then the `for`
command will return immediately.

The operation of `break` and `continue` are similar to the corresponding
statements in C.

`for` returns an empty string.

foreach
~~~~~~~
+*foreach* 'varName list body'+

+*foreach* 'varList list ?varList2 list2 \...? body'+

In this command, +'varName'+ is the name of a variable, +'list'+
is a list of values to assign to +'varName'+, and +'body'+ is a
collection of Tcl commands.

For each field in +'list'+ (in order from left to right), `foreach` assigns
the contents of the field to +'varName'+ (as if the `lindex` command
had been used to extract the field), then calls the Tcl interpreter to
execute +'body'+.

If instead of being a simple name, +'varList'+ is used, multiple assignments
are made each time through the loop, one for each element of +'varList'+.

For example, if there are two elements in +'varList'+ and six elements in
the list, the loop will be executed three times.

If the length of the list doesn't evenly divide by the number of elements
in +'varList'+, the value of the remaining variables in the last iteration
of the loop are undefined.

The `break` and `continue` statements may be invoked inside +'body'+,
with the same effect as in the `for` command.

`foreach` returns an empty string.

format
~~~~~~
+*format* 'formatString ?arg \...?'+

This command generates a formatted string in the same way as the
C 'sprintf' procedure (it uses 'sprintf' in its
implementation).  +'formatString'+ indicates how to format
the result, using +%+ fields as in 'sprintf', and the additional
arguments, if any, provide values to be substituted into the result.

All of the 'sprintf' options are valid; see the 'sprintf'
man page for details.  Each +'arg'+ must match the expected type
from the +%+ field in +'formatString'+; the `format` command
converts each argument to the correct type (floating, integer, etc.)
before passing it to 'sprintf' for formatting.

The only unusual conversion is for +%c+; in this case the argument
must be a decimal string, which will then be converted to the corresponding
ASCII (or UTF-8) character value.

In addition, Jim Tcl provides basic support for conversion to binary with +%b+.

`format` does backslash substitution on its +'formatString'+
argument, so backslash sequences in +'formatString'+ will be handled
correctly even if the argument is in braces.

The return value from `format` is the formatted string.

getref
~~~~~~
+*getref* 'reference'+

Returns the string associated with +'reference'+. The reference must
be a valid reference create with the `ref` command.

See <<_garbage_collection_references_lambda_function,GARBAGE COLLECTION>> for more detail.

gets
~~~~
+*gets* 'fileId ?varName?'+

+'fileId' *gets* '?varName?'+

Reads the next line from the file given by +'fileId'+ and discards
the terminating newline character.

If +'varName'+ is specified, then the line is placed in the variable
by that name and the return value is a count of the number of characters
read (not including the newline).

If the end of the file is reached before reading
any characters then -1 is returned and +'varName'+ is set to an
empty string.

If +'varName'+ is not specified then the return value will be
the line (minus the newline character) or an empty string if
the end of the file is reached before reading any characters.

An empty string will also be returned if a line contains no characters
except the newline, so `eof` may have to be used to determine
what really happened.

If the last character in the file is not a newline character, then
`gets` behaves as if there were an additional newline character
at the end of the file.

+'fileId'+ must be +stdin+ or the return value from a previous
call to `open`; it must refer to a file that was opened
for reading.

glob
~~~~
+*glob* ?*-nocomplain*? ?*-directory* 'dir'? ?*-tails*? ?*--*? 'pattern ?pattern \...?'+

This command performs filename globbing, using csh rules.  The returned
value from `glob` is the list of expanded filenames.

If +-nocomplain+ is specified as the first argument then an empty
list may be returned;  otherwise an error is returned if the expanded
list is empty.  The +-nocomplain+ argument must be provided
exactly: an abbreviation will not be accepted.

If +-directory+ is given, the +'dir'+ is understood to contain a
directory name to search in. This allows globbing inside directories
whose names may contain glob-sensitive characters. The returned names
include the directory name unless +'-tails'+ is specified.

If +'-tails'+ is specified, along with +-directory+, the returned names
are relative to the given directory.

global
~~~~~~

+*global* 'varName ?varName \...?'+

This command is ignored unless a Tcl procedure is being interpreted.
If so, then it declares each given +'varName'+ to be a global variable
rather than a local one.  For the duration of the current procedure
(and only while executing in the current procedure), any reference to
+'varName'+ will be bound to a global variable instead
of a local one.

An alternative to using `global` is to use the +::+ prefix
to explicitly name a variable in the global scope.

if
~~
+*if* 'expr1' ?*then*? 'body1' *elseif* 'expr2' ?*then*? 'body2' *elseif* \... ?*else*? ?'bodyN'?+

The `if` command evaluates +'expr1'+ as an expression (in the same way
that `expr` evaluates its argument).  The value of the expression must
be numeric; if it is non-zero then +'body1'+ is executed by passing it to
the Tcl interpreter.

Otherwise +'expr2'+ is evaluated as an expression and if it is non-zero
then +'body2'+ is executed, and so on.

If none of the expressions evaluates to non-zero then +'bodyN'+ is executed.

The +then+ and +else+ arguments are optional "noise words" to make the
command easier to read.

There may be any number of +elseif+ clauses, including zero.  +'bodyN'+
may also be omitted as long as +else+ is omitted too.

The return value from the command is the result of the body script that
was executed, or an empty string if none of the expressions was non-zero
and there was no +'bodyN'+.

incr
~~~~
+*incr* 'varName ?increment?'+

Increment the value stored in the variable whose name is +'varName'+.
The value of the variable must be integral.

If +'increment'+ is supplied then its value (which must be an
integer expression) is added to the value of variable +'varName'+;  otherwise
1 is added to +'varName'+.

The new value is stored as a decimal string in variable +'varName'+
and also returned as result.

If the variable does not exist, the variable is implicitly created
and set to +0+ first.

info
~~~~

+*info* 'option ?arg\...?'+::

Provide information about various internals to the Tcl interpreter.
The legal +'option'+'s (which may be abbreviated) are:

+*info args* 'procname'+::
    Returns a list containing the names of the arguments to procedure
    +'procname'+, in order.  +'procname'+ must be the name of a
    Tcl command procedure.

+*info alias* 'command'+::
    +'command'+ must be an alias created with `alias`. In which case the target
    command and arguments, as passed to `alias` are returned. See `exists -alias`

+*info body* 'procname'+::
    Returns the body of procedure +'procname'+.  +'procname'+ must be
    the name of a Tcl command procedure.

+*info channels*+::
    Returns a list of all open file handles from `open` or `socket`

+*info commands* ?'pattern'?+::
    If +'pattern'+ isn't specified, returns a list of names of all the
    Tcl commands, including both the built-in commands written in C and
    the command procedures defined using the `proc` command.
    If +'pattern'+ is specified, only those names matching +'pattern'+
    (using <<_string_matching,STRING MATCHING>> rules) are returned.

+*info complete* 'command' ?'missing'?+::
    Returns 1 if +'command'+ is a complete Tcl command in the sense of
    having no unclosed quotes, braces, brackets or array element names,
    If the command doesn't appear to be complete then 0 is returned.
    This command is typically used in line-oriented input environments
    to allow users to type in commands that span multiple lines;  if the
    command isn't complete, the script can delay evaluating it until additional
    lines have been typed to complete the command. If +'varName'+ is specified, the
    missing character is stored in the variable with that name.

+*info exists* 'varName'+::
    Returns '1' if the variable named +'varName'+ exists in the
    current context (either as a global or local variable), returns '0'
    otherwise.

+*info frame* ?'number'?+::
    If +'number'+ is not specified, this command returns a number
    which is the same result as `info level` - the current stack frame level.
    If +'number'+ is specified, then the result is a list consisting of the procedure,
    filename and line number for the procedure call at level +'number'+ on the stack.
    If +'number'+ is positive then it selects a particular stack level (1 refers
    to the top-most active procedure, 2 to the procedure it called, and
    so on); otherwise it gives a level relative to the current level
    (0 refers to the current procedure, -1 to its caller, and so on).
    The level has an identical meaning to `info level`.

+*info globals* ?'pattern'?+::
    If +'pattern'+ isn't specified, returns a list of all the names
    of currently-defined global variables.
    If +'pattern'+ is specified, only those names matching +'pattern'+
    (using <<_string_matching,STRING MATCHING>> rules) are returned.

+*info hostname*+::
    An alias for `os.gethostname` for compatibility with Tcl 6.x

+*info level* ?'number'?+::
    If +'number'+ is not specified, this command returns a number
    giving the stack level of the invoking procedure, or 0 if the
    command is invoked at top-level.  If +'number'+ is specified,
    then the result is a list consisting of the name and arguments for the
    procedure call at level +'number'+ on the stack.  If +'number'+
    is positive then it selects a particular stack level (1 refers
    to the top-most active procedure, 2 to the procedure it called, and
    so on); otherwise it gives a level relative to the current level
    (0 refers to the current procedure, -1 to its caller, and so on).
    See the `uplevel` command for more information on what stack
    levels mean.

+*info locals* ?'pattern'?+::
    If +'pattern'+ isn't specified, returns a list of all the names
    of currently-defined local variables, including arguments to the
    current procedure, if any.  Variables defined with the `global`
    and `upvar` commands will not be returned.  If +'pattern'+ is
    specified, only those names matching +'pattern'+
    (using <<_string_matching,STRING MATCHING>> rules) are returned.

+*info nameofexecutable*+::
    Returns the name of the binary file from which the application
    was invoked. A full path will be returned, unless the path
    can't be determined, in which case the empty string will be returned.

+*info procs* ?'pattern'?+::
    If +'pattern'+ isn't specified, returns a list of all the
    names of Tcl command procedures.
    If +'pattern'+ is specified, only those names matching +'pattern'+
    (using <<_string_matching,STRING MATCHING>> rules) are returned.

+*info references*+::
    Returns a list of all references which have not yet been garbage
    collected.

+*info returncodes* ?'code'?+::
    Returns a list representing the mapping of standard return codes
    to names. e.g. +{0 ok 1 error 2 return \...}+. If a code is given,
    instead returns the name for the given code.

+*info script*+::
    If a Tcl script file is currently being evaluated (i.e. there is a
    call to 'Jim_EvalFile' active or there is an active invocation
    of the `source` command), then this command returns the name
    of the innermost file being processed.  Otherwise the command returns an
    empty string.

+*info source* 'script ?filename line?'+::
    With a single argument, returns the original source location of the given script as a list of
    +{filename linenumber}+. If the source location can't be determined, the
    list +{{} 0}+ is returned. If +'filename'+ and +'line'+ are given, returns a copy
    of +'script'+ with the associate source information. This can be useful to produce
    useful messages from `eval`, etc. if the original source information may be lost.

+*info stacktrace*+::
    After an error is caught with `catch`, returns the stack trace as a list
    of +{procedure filename line \...}+.

+*info statics* 'procname'+::
    Returns a dictionary of the static variables of procedure
    +'procname'+.  +'procname'+ must be the name of a Tcl command
    procedure. An empty dictionary is returned if the procedure has
    no static variables.

+*info version*+::
    Returns the version number for this version of Jim in the form +*x.yy*+.

+*info vars* ?'pattern'?+::
    If +'pattern'+ isn't specified,
    returns a list of all the names of currently-visible variables, including
    both locals and currently-visible globals.
    If +'pattern'+ is specified, only those names matching +'pattern'+
    (using <<_string_matching,STRING MATCHING>> rules) are returned.

join
~~~~
+*join* 'list ?joinString?'+

The +'list'+ argument must be a valid Tcl list.  This command returns the
string formed by joining all of the elements of +'list'+ together with
+'joinString'+ separating each adjacent pair of elements.

The +'joinString'+ argument defaults to a space character.

kill
~~~~
+*kill* ?'SIG'|*-0*? 'pid'+

Sends the given signal to the process identified by +'pid'+.

The signal may be specified by name or number in one of the following forms:

* +TERM+
* +SIGTERM+
* +-TERM+
* +15+
* +-15+

The signal name may be in either upper or lower case.

The special signal name +-0+ simply checks that a signal +'could'+ be sent.

If no signal is specified, SIGTERM is used.

An error is raised if the signal could not be delivered.

lambda
~~~~~~
+*lambda* 'args ?statics? body'+

The `lambda` command is identical to `proc`, except rather than
creating a named procedure, it creates an anonymous procedure and returns
the name of the procedure.

See `proc` and <<_garbage_collection_references_lambda_function,GARBAGE COLLECTION>> for more detail.

lappend
~~~~~~~
+*lappend* 'varName value ?value value \...?'+

Treat the variable given by +'varName'+ as a list and append each of
the +'value'+ arguments to that list as a separate element, with spaces
between elements.

If +'varName'+ doesn't exist, it is created as a list with elements given
by the +'value'+ arguments. `lappend` is similar to `append` except that
each +'value'+ is appended as a list element rather than raw text.

This command provides a relatively efficient way to build up large lists.
For example,

----
    lappend a $b
----

is much more efficient than

----
    set a [concat $a [list $b]]
----

when +$a+ is long.

lassign
~~~~~~~
+*lassign* 'list varName ?varName \...?'+

This command treats the value +'list'+ as a list and assigns successive elements from that list to
the variables given by the +'varName'+ arguments in order. If there are more variable names than
list elements, the remaining variables are set to the empty string. If there are more list elements
than variables, a list of unassigned elements is returned.

----
    . lassign {1 2 3} a b; puts a=$a,b=$b
    3
    a=1,b=2
----

local
~~~~~
+*local* 'cmd ?arg\...?'+

First, `local` evaluates +'cmd'+ with the given arguments. The return value must
be the name of an existing command, which is then marked as having local scope.
This means that when the current procedure exits, the specified
command is deleted. This can be useful with `lambda`, local procedures or
to automatically close a filehandle.

In addition, if a the command already exists with the same name,
the existing command will be kept rather than being deleted, and may be called
via `upcall`. The previous command will be restored when the current
procedure exits. See `upcall` for more details.

In this example, a local procedure is created. Note that the procedure
continues to have global scope while it is active.

----
    proc outer {} {
      # proc ... returns "inner" which is marked local
      local proc inner {} {
        # will be deleted when 'outer' exits
      }

      inner
      ...
    }
----

In this example, the lambda is deleted at the end of the procedure rather
than waiting until garbage collection.

----
    proc outer {} {
      set x [lambda inner {args} {
        # will be deleted when 'outer' exits
      }]
      # Use 'function' here which simply returns $x
      local function $x

      $x ...
      ...
    }
----

Also see `defer` as another mechanism for cleaning up at the end of a procedure.

loop
~~~~
+*loop* 'var ?first? limit ?incr? body'+

Similar to `for` except simpler and possibly more efficient.
If +'incr'+ is positive, the effect is, equivalent to:

----
    for {set var $first} {$var < $limit} {incr var $incr} $body
----

While if +'incr'+ is negative, the count is downwards.

If +'first'+ is not specified, 0 is used.
If +'incr'+ is not specified, 1 is used.
Note that setting the loop variable inside the loop does not
affect the loop count.

+'first'+, +'limit'+ and +'incr'+ may be any integer expression.

lindex
~~~~~~
+*lindex* 'list ?index ...?'+

Treats +'list'+ as a Tcl list and returns element +'index'+ from it
(0 refers to the first element of the list).
See <<_string_and_list_index_specifications,STRING AND LIST INDEX SPECIFICATIONS>> for all allowed forms for +'index'+.

In extracting the element, +'lindex'+ observes the same rules concerning
braces and quotes and backslashes as the Tcl command interpreter; however,
variable substitution and command substitution do not occur.

If no index values are given, simply returns +'list'+

If +'index'+ is negative or greater than or equal to the number of elements
in +'list'+, then an empty string is returned.

If additional index arguments are supplied, then each argument is
used in turn to select an element from the previous indexing
operation, allowing the script to select elements from sublists.

linsert
~~~~~~~
+*linsert* 'list index element ?element element \...?'+

This command produces a new list from +'list'+ by inserting all
of the +'element'+ arguments just before the element +'index'+
of +'list'+. Each +'element'+ argument will become
a separate element of the new list. If +'index'+ is less than
or equal to zero, then the new elements are inserted at the
beginning of the list. If +'index'+ is greater than or equal
to the number of elements in the list, then the new elements are
appended to the list.

See <<_string_and_list_index_specifications,STRING AND LIST INDEX SPECIFICATIONS>> for all allowed forms for +'index'+.

list
~~~~

+*list* 'arg ?arg \...?'+

This command returns a list comprised of all the arguments, +'arg'+. Braces
and backslashes get added as necessary, so that the `lindex` command
may be used on the result to re-extract the original arguments, and also
so that `eval` may be used to execute the resulting list, with
+'arg1'+ comprising the command's name and the other args comprising
its arguments. `list` produces slightly different results than
`concat`:  `concat` removes one level of grouping before forming
the list, while `list` works directly from the original arguments.
For example, the command

----
    list a b {c d e} {f {g h}}
----

will return

----
    a b {c d e} {f {g h}}
----

while `concat` with the same arguments will return

----
    a b c d e f {g h}
----

llength
~~~~~~~
+*llength* 'list'+

Treats +'list'+ as a list and returns the number of elements in that list.

lset
~~~~
+*lset* 'varName ?index ..? newValue'+

Sets an element in a list.

The `lset` command accepts a parameter, +'varName'+, which it interprets
as the name of a variable containing a Tcl list. It also accepts
zero or more indices into the list. Finally, it accepts a new value
for an element of +'varName'+. If no indices are presented, the command
takes the form:

----
    lset varName newValue
----

In this case, newValue replaces the old value of the variable
+'varName'+.

When presented with a single index, the `lset` command
treats the content of the +'varName'+ variable as a Tcl list. It addresses
the index'th element in it (0 refers to the first element of the
list). When interpreting the list, `lset` observes the same rules
concerning braces and quotes and backslashes as the Tcl command
interpreter; however, variable substitution and command substitution
do not occur. The command constructs a new list in which the
designated element is replaced with newValue. This new list is
stored in the variable +'varName'+, and is also the return value from
the `lset` command.

If index is negative or greater than or equal to the number of
elements in +$varName+, then an error occurs.

See <<_string_and_list_index_specifications,STRING AND LIST INDEX SPECIFICATIONS>> for all allowed forms for +'index'+.

If additional index arguments are supplied, then each argument is
used in turn to address an element within a sublist designated by
the previous indexing operation, allowing the script to alter
elements in sublists. The command,

----
    lset a 1 2 newValue
----

replaces element 2 of sublist 1 with +'newValue'+.

The integer appearing in each index argument must be greater than
or equal to zero. The integer appearing in each index argument must
be strictly less than the length of the corresponding list. In other
words, the `lset` command cannot change the size of a list. If an
index is outside the permitted range, an error is reported.

lmap
~~~~

+*lmap* 'varName list body'+

+*lmap* 'varList list ?varList2 list2 \...? body'+

`lmap` is a "collecting" `foreach` which returns a list of its results.

For example:

----
    . lmap i {1 2 3 4 5} {expr $i*$i}
    1 4 9 16 25
    . lmap a {1 2 3} b {A B C} {list $a $b}
    {1 A} {2 B} {3 C}
----

If the body invokes `continue`, no value is added for this iteration.
If the body invokes `break`, the loop ends and no more values are added.

load
~~~~
+*load* 'filename'+

Loads the dynamic extension, +'filename'+. Generally the filename should have
the extension +.so+. The initialisation function for the module must be based
on the name of the file. For example loading +hwaccess.so+ will invoke
the initialisation function, +Jim_hwaccessInit+. Normally the `load` command
should not be used directly. Instead it is invoked automatically by `package require`.

lrange
~~~~~~
+*lrange* 'list first last'+

+'list'+ must be a valid Tcl list. This command will return a new
list consisting of elements +'first'+ through +'last'+, inclusive.

See <<_string_and_list_index_specifications,STRING AND LIST INDEX SPECIFICATIONS>> for all allowed forms for +'first'+ and +'last'+.

If +'last'+ is greater than or equal to the number of elements
in the list, then it is treated as if it were +end+.

If +'first'+ is greater than +'last'+ then an empty string
is returned.

Note: +"`lrange` 'list first first'"+ does not always produce the
same result as +"`lindex` 'list first'"+ (although it often does
for simple fields that aren't enclosed in braces); it does, however,
produce exactly the same results as +"`list` [`lindex` 'list first']"+

lreplace
~~~~~~~~

+*lreplace* 'list first last ?element element \...?'+

Returns a new list formed by replacing one or more elements of
+'list'+ with the +'element'+ arguments.

+'first'+ gives the index in +'list'+ of the first element
to be replaced.

If +'first'+ is less than zero then it refers to the first
element of +'list'+;  the element indicated by +'first'+
must exist in the list.

+'last'+ gives the index in +'list'+ of the last element
to be replaced;  it must be greater than or equal to +'first'+.

See <<_string_and_list_index_specifications,STRING AND LIST INDEX SPECIFICATIONS>> for all allowed forms for +'first'+ and +'last'+.

The +'element'+ arguments specify zero or more new arguments to
be added to the list in place of those that were deleted.

Each +'element'+ argument will become a separate element of
the list.

If no +'element'+ arguments are specified, then the elements
between +'first'+ and +'last'+ are simply deleted.

lrepeat
~~~~~~~~
+*lrepeat* 'number element1 ?element2 \...?'+

Build a list by repeating elements +'number'+ times (which must be
a positive integer).

----
    . lrepeat 3 a b
    a b a b a b
----

lreverse
~~~~~~~~
+*lreverse* 'list'+

Returns the list in reverse order.

----
    . lreverse {1 2 3}
    3 2 1
----

lsearch
~~~~~~~
+*lsearch* '?options? list pattern'+

This command searches the elements +'list'+ to see if one of them matches +'pattern'+. If so, the
command returns the index of the first matching element (unless the options +-all+, +-inline+ or +-bool+ are
specified.) If not, the command returns -1. The option arguments indicates how the elements of
the list are to be matched against pattern and must have one of the values below:

*Note* that this command is different from Tcl in that default match type is +-exact+ rather than +-glob+.

+*-exact*+::
    +'pattern'+ is a literal string that is compared for exact equality against each list element.
    This is the default.

+*-glob*+::
    +'pattern'+ is a glob-style pattern which is matched against each list element using
    <<_string_matching,STRING MATCHING>> rules.

+*-regexp*+::
    +'pattern'+ is treated as a regular expression and matched against each list element using
    <<_regular_expressions,REGULAR EXPRESSIONS>> rules.

+*-command* 'cmdname'+::
    +'cmdname'+ is a command which is used to match the pattern against each element of the
    list. It is invoked as +'cmdname' ?*-nocase*? 'pattern listvalue'+ and should return 1
    for a match, or 0 for no match.

+*-all*+::
    Changes the result to be the list of all matching indices (or all matching values if
    +-inline+ is specified as well). If indices are returned, the indices will be in numeric
    order. If values are returned, the order of the values will be the order of those values
    within the input list.

+*-inline*+::
    The matching value is returned instead of its index (or an empty string if no value
    matches). If +-all+ is also specified, then the result of the command is the list of all
    values that matched. The +-inline+ and +-bool+ options are mutually exclusive.

+*-bool*+::
    Changes the result to '1' if a match was found, or '0' otherwise. If +-all+ is also specified,
    the result will be a list of '0' and '1' for each element of the list depending upon whether
    the corresponding element matches. The +-inline+ and +-bool+ options are mutually exclusive.

+*-not*+::
    This negates the sense of the match, returning the index (or value
    if +-inline+ is specified) of the first non-matching value in the
    list. If +-bool+ is also specified, the '0' will be returned if a
    match is found, or '1' otherwise. If +-all+ is also specified,
    non-matches will be returned rather than matches.

+*-nocase*+::
    Causes comparisons to be handled in a case-insensitive manner.

+*-index* 'indexList'+::
    This option is designed for use when searching within nested lists. The
    'indexList' gives a path of indices (much as might be used with
    the lindex or lset commands) within each element to allow the location
    of the term being matched against.

+*-stride* 'strideLength'+::
    If this option is specified, the list is treated as consisting of
    groups of 'strideLength' elements and the groups are searched by
    either their first element or, if the +-index+ option is used,
    by the element within each group given by the first index passed to
    +-index+ (which is then ignored by +-index+). The resulting
    index always points to the first element in a group.
 ::
    The list length must be an integer multiple of 'strideLength', which
    in turn must be at least 1. A 'strideLength' of 1 is the default and
    indicates no grouping.

lsort
~~~~~
+*lsort* '?options? list'+

Sort the elements of +'list'+, returning a new list in sorted order.
By default, ASCII (or UTF-8) sorting is used, with the result in increasing order.

Note that only one sort type may be selected with +-integer+, +-real+, +-nocase+ or +-command+
with last option being used.

+*-integer*+::
    Sort using numeric (integer) comparison.

+*-real*+::
    Sort using floating point comparison.

+*-nocase*+::
    Sort using using string comparison without regard for case.

+*-command* 'cmdname'+::
    +'cmdname'+ is treated as a command name. For each comparison,
    +'cmdname $value1 $value2+' is called which
    should compare the values and return an integer less than, equal
    to, or greater than zero if the +'$value1'+ is to be considered less
    than, equal to, or greater than +'$value2'+, respectively.

+*-increasing*+::
    The resulting list is in ascending order, from smallest/lowest to largest/highest.
    This is the default and does not need to be specified.

+*-decreasing*+::
    The resulting list is in the opposite order to what it would be otherwise.

+*-unique*+::
    Only the last set of duplicate elements found in the list will
    be retained.  Note that duplicates are determined relative to the
    comparison used in the sort. Thus if +-index 0+ is used, +{1 a}+ and
    +{1 b}+ would be considered duplicates and only the second element,
    +{1 b}+, would be retained.

+*-index* 'indexList'+::
    This option is designed for use when sorting nested lists. The
    'indexList' gives a path of indices (much as might be used with
    the lindex or lset commands) within each element to specify the
    value to be used for comparison.

+*-stride* 'strideLength'+::
    If this option is specified, the list is treated as consisting of
    groups of 'strideLength' elements and the groups are sorted by
    either their first element or, if the +-index+ option is used,
    by the element within each group given by the first index passed to
    +-index+ (which is then ignored by +-index+). The resulting list
    is once again a flat list.
 ::
    The list length must be an integer multiple of 'strideLength', which
    in turn must be at least 2.

defer
~~~~~
+*defer* 'script'+

This command is a simple helper command to add a script to the '+$jim::defer+' variable
that will run when the current proc or interpreter exits. For example:

----
    . proc a {} { defer {puts "Leaving a"}; puts "Exit" }
    . a
    Exit
    Leaving a
----

If the '+$jim::defer+' variable exists, it is treated as a list of scripts to run
when the proc or interpreter exits.

open
~~~~
+*open* 'fileName ?access?'+

+*open* '|command-pipeline ?access?'+

Opens a file and returns an identifier
that may be used in future invocations
of commands like `read`, `puts`, and `close`.
+'fileName'+ gives the name of the file to open.

The +'access'+ argument indicates the way in which the file is to be accessed.
It may have any of the following values:

+r+::
    Open the file for reading only; the file must already exist.

+r++::
    Open the file for both reading and writing; the file must
    already exist.

+w+::
    Open the file for writing only. Truncate it if it exists. If it doesn't
    exist, create a new file.

+w++::
    Open the file for reading and writing. Truncate it if it exists.
    If it doesn't exist, create a new file.

+a+::
    Open the file for writing only. The file must already exist, and the file
    is positioned so that new data is appended to the file.

+a++::
    Open the file for reading and writing. If the file doesn't
    exist, create a new empty file. Set the initial access position
    to the end of the file.

+'access'+ defaults to 'r'.

Additionally, if POSIX mode is supported by the underlying system,
then access may insted of consistent of a list of any of the following
flags, all of which have the standard POSIX meanings. In this case,
the first flag *must* be one of RDONLY, WRONLY or RDWR.

+RDONLY+::
    Open the file for reading only.

+WRONLY+::
    Open the file for writing only.

+RDWR+::
    Open the file for both reading and writing.

+APPEND+::
    Set the file pointer to the end of the file prior to each write.

+BINARY+::
    Ignored.

+CREAT+::
    Create the file if it does not already exist (without this flag
    it  is  an  error for the file not to exist).

+EXCL+::
    If CREAT is also specified, an error is returned if the file
    already exists.

+NOCTTY+::
    If  the  file is a terminal device, this flag prevents the file
    from becoming the controlling terminal of the process.

+TRUNC+::
    If the file exists it is truncated to zero length.

If a file is opened for both reading and writing, then `seek`
must be invoked between a read and a write, or vice versa.

If the first character of +'fileName'+ is "|" then the remaining
characters of +'fileName'+ are treated as a list of arguments that
describe a command pipeline to invoke, in the same style as the
arguments for exec. In this case, the channel identifier returned
by open may be used to write to the command's input pipe or read
from its output pipe, depending on the value of +'access'+. If write-only
access is used (e.g. +'access'+ is 'w'), then standard output for the
pipeline is directed to the current standard output unless overridden
by the command. If read-only access is used (e.g. +'access'+ is r),
standard input for the pipeline is taken from the current standard
input unless overridden by the command.

The `pid` command may be used to return the process ids of the commands
forming the command pipeline.

See also `socket`, `pid`, `exec`

package
~~~~~~~
+*package provide* 'name ?version?'+

Indicates that the current script provides the package named +'name'+.
*Note*: The supplied version is ignored. All packages are registered as version 1.0
(it is simply accepted for compatibility purposes).

Any script that provides a package may include this statement
as the first statement, although it is not required.

+*package require* 'name ?version?'+

Searches for the package with the given +'name'+ by examining each path
in '$::auto_path' and trying to load '$path/$name.so' as a dynamic extension,
or '$path/$name.tcl' as a script package.

The first such file which is found is considered to provide the package.
(The version number is ignored).

If '$name.so' exists, it is loaded with the `load` command,
otherwise if '$name.tcl' exists it is loaded with the `source` command.

If `load` or `source` fails, `package require` will fail immediately.
No further attempt will be made to locate the file.

+*package names*+

Returns a list of all known/loaded packages, including internal packages.

pid
~~~
+*pid*+

+*pid* 'fileId'+

The first form returns the process identifier of the current process.

The second form accepts a handle returned by `open` and returns a list
of the process ids forming the pipeline in the same form as `exec ... &`.
If 'fileId' represents a regular file handle rather than a command pipeline,
the empty string is returned instead.

See also `open`, `exec`

proc
~~~~
+*proc* 'name args ?statics? body'+

The `proc` command creates a new Tcl command procedure, +'name'+.
When the new command is invoked, the contents of +'body'+ will be executed.
Tcl interpreter. +'args'+ specifies the formal arguments to the procedure.
If specified, +'statics'+, declares static variables which are bound to the
procedure.

See <<_procedures,PROCEDURES>> for detailed information about Tcl procedures.

The `proc` command returns +'name'+ (which is useful with `local`).

When a procedure is invoked, the procedure's return value is the
value specified in a `return` command.  If the procedure doesn't
execute an explicit `return`, then its return value is the value
of the last command executed in the procedure's body.

If an error occurs while executing the procedure body, then the
procedure-as-a-whole will return that same error.

puts
~~~~
+*puts* ?*-nonewline*? '?fileId? string'+

+'fileId' *puts* ?*-nonewline*? 'string'+

Writes the characters given by +'string'+ to the file given
by +'fileId'+. +'fileId'+ must have been the return
value from a previous call to `open`, or it may be
+stdout+ or +stderr+ to refer to one of the standard I/O
channels; it must refer to a file that was opened for
writing.

In the first form, if no +'fileId'+ is specified then it defaults to +stdout+.
`puts` normally outputs a newline character after +'string'+,
but this feature may be suppressed by specifying the +-nonewline+
switch.

Output to files is buffered internally by Tcl; the `flush`
command may be used to force buffered characters to be output.

pipe
~~~~
Creates a pair of `aio` channels and returns the handles as a list: +{read write}+

----
    lassign [pipe] r w

    # Must close $w after exec
    exec ps >@$w &
    $w close

    $r readable ...
----

pwd
~~~
+*pwd*+

Returns the path name of the current working directory.

rand
~~~~
+*rand* '?min? ?max?'+

Returns a random integer between +'min'+ (defaults to 0) and +'max'+
(defaults to the maximum integer).

If only one argument is given, it is interpreted as +'max'+.

range
~~~~
+*range* '?start? end ?step?'+

Returns a list of integers starting at +'start'+ (defaults to 0)
and ranging up to but not including +'end'+ in steps of +'step'+ defaults to 1).

----
    . range 5
    0 1 2 3 4
    . range 2 5
    2 3 4
    . range 2 10 4
    2 6
    . range 7 4 -2
    7 5
----

Integer parameters may be any integer expression.

read
~~~~
+*read* ?*-nonewline*? 'fileId'+

+'fileId' *read* ?*-nonewline*?+

+*read* 'fileId numBytes'+

+'fileId' *read* 'numBytes'+

+*read* ?*-pending*? 'fileId'+

+'fileId' *read* ?*-pending*?+

In the first form, all of the remaining bytes are read from the file
given by +'fileId'+; they are returned as the result of the command.
If the +-nonewline+ switch is specified then the last
character of the file is discarded if it is a newline.

In the second form, the extra argument specifies how many bytes to read;
exactly this many bytes will be read and returned, unless there are fewer than
+'numBytes'+ bytes left in the file; in this case, all the remaining
bytes are returned.

The third form is currently only useful with SSL sockets. It reads at least 1 byte
and then any additional data that is buffered. This allows for use in an event handler.
e.g.

----
    $sock readable {
        set buf [$sock read -pending]
    }
----

This is necessary because otherwise pending data may be buffered, but
the underlying socket will not be marked 'readable'. This featured is not
currently supported for regular sockets, and so these sockets must be
set to unbufferred (+$sock buffering false+) to work in an event loop.

+'fileId'+ must be +stdin+ or the return value from a previous call
to `open`; it must refer to a file that was opened for reading.

regexp
~~~~~~
+*regexp ?-nocase? ?-line? ?-indices? ?-start* 'offset'? *?-all? ?-inline? ?--?* 'exp string ?matchVar? ?subMatchVar subMatchVar \...?'+

Determines whether the regular expression +'exp'+ matches part or
all of +'string'+ and returns 1 if it does, 0 if it doesn't.

See <<_regular_expressions,REGULAR EXPRESSIONS>> above for complete information on the
syntax of +'exp'+ and how it is matched against +'string'+.

If additional arguments are specified after +'string'+ then they
are treated as the names of variables to use to return
information about which part(s) of +'string'+ matched +'exp'+.
+'matchVar'+ will be set to the range of +'string'+ that
matched all of +'exp'+. The first +'subMatchVar'+ will contain
the characters in +'string'+ that matched the leftmost parenthesized
subexpression within +'exp'+, the next +'subMatchVar'+ will
contain the characters that matched the next parenthesized
subexpression to the right in +'exp'+, and so on.

Normally, +'matchVar'+ and the each +'subMatchVar'+ are set to hold the
matching characters from `string`, however see +-indices+ and
+-inline+ below.

If there are more values for +'subMatchVar'+ than parenthesized subexpressions
within +'exp'+, or if a particular subexpression in +'exp'+ doesn't
match the string (e.g. because it was in a portion of the expression
that wasn't matched), then the corresponding +'subMatchVar'+ will be
set to +"-1 -1"+ if +-indices+ has been specified or to an empty
string otherwise.

The following switches modify the behaviour of +'regexp'+

+*-nocase*+::
    Causes upper-case and lower-case characters to be treated as
    identical during the matching process.

+*-line*+::
    Use newline-sensitive matching. By default, newline
    is a completely ordinary character with no special meaning in
    either REs or strings. With this flag, +[^+ bracket expressions
    and +.+ never match newline, an +^+ anchor matches the empty
    string after any newline in the string in addition to its normal
    function, and the +$+ anchor matches the empty string before any
    newline in the string in addition to its normal function.

+*-indices*+::
    Changes what is stored in the subMatchVars. Instead of
    storing the matching characters from string, each variable
    will contain a list of two decimal strings giving the indices
    in string of the first and last characters in the matching
    range of characters.

+*-start* 'offset'+::
    Specifies a character index offset into the string at which to start
    matching the regular expression. If +-indices+ is
    specified, the indices will be indexed starting from the
    absolute beginning of the input string. +'offset'+ will be
    constrained to the bounds of the input string.

+*-all*+::
    Causes the regular expression to be matched as many times as possible
    in the string, returning the total number of matches found. If this
    is specified with match variables, they will contain information
    for the last match only.

+*-inline*+::
    Causes the command to return, as a list, the data that would otherwise
    be placed in match variables. When using +-inline+, match variables
    may not be specified. If used with +-all+, the list will be concatenated
    at each iteration, such that a flat list is always returned. For
    each match iteration, the command will append the overall match
    data, plus one element for each subexpression in the regular
    expression.

+*--*+::
    Marks the end of switches. The argument following this one will be
    treated as +'exp'+ even if it starts with a +-+.

regsub
~~~~~~
+*regsub ?-nocase? ?-all? ?-line? ?-start* 'offset'? ?*--*? 'exp string subSpec ?varName?'+

This command matches the regular expression +'exp'+ against
+'string'+ using the rules described in REGULAR EXPRESSIONS
above.

If +'varName'+ is specified, the commands stores +'string'+ to +'varName'+
with the substitutions detailed below, and returns the number of
substitutions made (normally 1 unless +-all+ is specified).
This is 0 if there were no matches.

If +'varName'+ is not specified, the substituted string will be returned
instead.

When copying +'string'+, the portion of +'string'+ that
matched +'exp'+ is replaced with +'subSpec'+.
If +'subSpec'+ contains a +&+ or +{backslash}0+, then it is replaced
in the substitution with the portion of +'string'+ that
matched +'exp'+.

If +'subSpec'+ contains a +{backslash}n+, where +'n'+ is a digit
between 1 and 9, then it is replaced in the substitution with
the portion of +'string'+ that matched the +'n'+\'-th
parenthesized subexpression of +'exp'+.
Additional backslashes may be used in +'subSpec'+ to prevent special
interpretation of +&+ or +{backslash}0+ or +{backslash}n+ or
backslash.

The use of backslashes in +'subSpec'+ tends to interact badly
with the Tcl parser's use of backslashes, so it's generally
safest to enclose +'subSpec'+ in braces if it includes
backslashes.

The following switches modify the behaviour of +'regsub'+

+*-nocase*+::
    Upper-case characters in +'string'+ are converted to lower-case
    before matching against +'exp'+;  however, substitutions
    specified by +'subSpec'+ use the original unconverted form
    of +'string'+.

+*-all*+::
    All ranges in +'string'+ that match +'exp'+ are found and substitution
    is performed for each of these ranges, rather than only the
    first. The +&+ and +{backslash}n+ sequences are handled for
    each substitution using the information from the corresponding
    match.

+*-line*+::
    Use newline-sensitive matching. By default, newline
    is a completely ordinary character with no special meaning in
    either REs or strings.  With this flag, +[^+ bracket expressions
    and +.+ never match newline, an +^+ anchor matches the empty
    string after any newline in the string in addition to its normal
    function, and the +$+ anchor matches the empty string before any
    newline in the string in addition to its normal function.

+*-start* 'offset'+::
    Specifies a character index offset into the string at which to
    start matching the regular expression. +'offset'+ will be
    constrained to the bounds of the input string.

+*--*+::
    Marks the end of switches. The argument following this one will be
    treated as +'exp'+ even if it starts with a +-+.

ref
~~~
+*ref* 'string tag ?finalizer?'+

Create a new reference containing +'string'+ of type +'tag'+.
If +'finalizer'+ is specified, it is a command which will be invoked
when the a garbage collection cycle runs and this reference is
no longer accessible.

The finalizer is invoked as:

----
    finalizer reference string
----

See <<_garbage_collection_references_lambda_function,GARBAGE COLLECTION>> for more detail.

rename
~~~~~~
+*rename* 'oldName newName'+

Rename the command that used to be called +'oldName'+ so that it
is now called +'newName'+.  If +'newName'+ is an empty string
(e.g. {}) then +'oldName'+ is deleted.  The `rename` command
returns an empty string as result.

return
~~~~~~
+*return* ?*-code* 'code'? ?*-errorinfo* 'stacktrace'? ?*-errorcode* 'errorcode'? ?*-level* 'n'? ?'value'?+

Return immediately from the current procedure (or top-level command
or `source` command), with +'value'+ as the return value.  If +'value'+
is not specified, an empty string will be returned as result.

If +-code+ is specified (as either a number or ok, error, break,
continue, signal, return or exit), this code will be used instead
of +JIM_OK+. This is generally useful when implementing flow of control
commands.

If +-level+ is specified and greater than 1, it has the effect of delaying
the new return code from +-code+. This is useful when rethrowing an error
from `catch`. See the implementation of try/catch in tclcompat.tcl for
an example of how this is done.

Note: The following options are only used when +-code+ is JIM_ERR.

If +-errorinfo+ is specified (as returned from `info stacktrace`)
it is used to initialize the stacktrace.

If +-errorcode+ is specified, it is used to set the global variable $::errorCode.

scan
~~~~
+*scan* 'string format varName1 ?varName2 \...?'+

This command parses fields from an input string in the same fashion
as the C 'sscanf' procedure.  +'string'+ gives the input to be parsed
and +'format'+ indicates how to parse it, using '%' fields as in
'sscanf'.  All of the 'sscanf' options are valid; see the 'sscanf'
man page for details.  Each +'varName'+ gives the name of a variable;
when a field is scanned from +'string'+, the result is converted back
into a string and assigned to the corresponding +'varName'+.  The
only unusual conversion is for '%c'.  For '%c' conversions a single
character value is converted to a decimal string, which is then
assigned to the corresponding +'varName'+; no field width may be
specified for this conversion.

seek
~~~~
+*seek* 'fileId offset ?origin?'+

+'fileId' *seek* 'offset ?origin?'+

Change the current access position for +'fileId'+.
The +'offset'+ and +'origin'+ arguments specify the position at
which the next read or write will occur for +'fileId'+.
+'offset'+ must be a number (which may be negative) and +'origin'+
must be one of the following:

+*start*+::
    The new access position will be +'offset'+ bytes from the start
    of the file.

+*current*+::
    The new access position will be +'offset'+ bytes from the current
    access position; a negative +'offset'+ moves the access position
    backwards in the file.

+*end*+::
    The new access position will be +'offset'+ bytes from the end of
    the file.  A negative +'offset'+ places the access position before
    the end-of-file, and a positive +'offset'+ places the access position
    after the end-of-file.

The +'origin'+ argument defaults to +start+.

+'fileId'+ must have been the return value from a previous call to
`open`, or it may be +stdin+, +stdout+, or +stderr+ to refer to one
of the standard I/O channels.

This command returns an empty string.

set
~~~
+*set* 'varName ?value?'+

Returns the value of variable +'varName'+.

If +'value'+ is specified, then set the value of +'varName'+ to +'value'+,
creating a new variable if one doesn't already exist, and return
its value.

If +'varName'+ contains an open parenthesis and ends with a
close parenthesis, then it refers to an array element:  the characters
before the open parenthesis are the name of the array, and the characters
between the parentheses are the index within the array.
Otherwise +'varName'+ refers to a scalar variable.

If no procedure is active, then +'varName'+ refers to a global
variable.

If a procedure is active, then +'varName'+ refers to a parameter
or local variable of the procedure, unless the +'global'+ command
has been invoked to declare +'varName'+ to be global.

The +::+ prefix may also be used to explicitly reference a variable
in the global scope.

setref
~~~~~~
+*setref* 'reference string'+

Store a new string in +'reference'+, replacing the existing string.
The reference must be a valid reference create with the `ref`
command.

See <<_garbage_collection_references_lambda_function,GARBAGE COLLECTION>> for more detail.

signal
~~~~~~
Command for signal handling.

See `kill` for the different forms which may be used to specify signals.

Commands which return a list of signal names do so using the canonical form:
"+SIGINT SIGTERM+".

+*signal handle* ?'signals \...'?+::
    If no signals are given, returns a list of all signals which are currently
    being handled.
    If signals are specified, these are added to the list of signals currently
    being handled.

+*signal ignore* ?'signals \...'?+::
    If no signals are given, returns a lists all signals which are currently
    being ignored.
    If signals are specified, these are added to the list of signals
    currently being ignored. These signals are still delivered, but
    are not considered by `catch -signal` or `try -signal`. Use
    `signal check` to determine which signals have occurred but
    been ignored.

+*signal block* ?'signals \...'?+::
    If no signals are given, returns a lists all signals which are currently
    being blocked.
    If signals are specified, these are added to the list of signals
    currently being blocked. These signals are not delivered to the process.
    This can be useful for signals such as +SIGPIPE+, especially in conjunction
    with `exec` as child processes inherit the parent's signal disposition.

+*signal default* ?'signals \...'?+::
    If no signals are given, returns a lists all signals which currently have
    the default behaviour.
    If signals are specified, these are added to the list of signals which have
    the default behaviour.

+*signal check ?-clear?* ?'signals \...'?+::
    Returns a list of signals which have been delivered to the process
    but are 'ignored'. If signals are specified, only that set of signals will
    be checked, otherwise all signals will be checked.
    If +-clear+ is specified, any signals returned are removed and will not be
    returned by subsequent calls to `signal check` unless delivered again.

+*signal throw* ?'signal'?+::
    Raises the given signal, which defaults to +SIGINT+ if not specified.
    The behaviour is identical to:

----
    kill signal [pid]
----

Note that `signal handle` and `signal ignore` represent two forms of signal
handling. `signal handle` is used in conjunction with `catch -signal` or `try -signal`
to immediately abort execution when the signal is delivered. Alternatively, `signal ignore`
is used in conjunction with `signal check` to handle signal synchronously. Consider the
two examples below.

Prevent a processing from taking too long

----
    signal handle SIGALRM
    alarm 20
    try -signal {
        .. possibly long running process ..
        alarm 0
    } on signal {sig} {
        puts stderr "Process took too long"
    }
----

Handle SIGHUP to reconfigure:

----
    signal ignore SIGHUP
    while {1} {
        ... handle configuration/reconfiguration ...
        while {[signal check -clear SIGHUP] eq ""} {
            ... do processing ..
        }
        # Received SIGHUP, so reconfigure
    }
----

Note: signal handling is currently not supported in child interpreters.
In these interpreters, the signal command does not exist.

sleep
~~~~~
+*sleep* 'seconds'+

Pauses for the given number of seconds, which may be a floating
point value less than one to sleep for less than a second, or an
integer to sleep for one or more seconds.

source
~~~~~~
+*source* 'fileName'+

Read file +'fileName'+ and pass the contents to the Tcl interpreter
as a sequence of commands to execute in the normal fashion.  The return
value of `source` is the return value of the last command executed
from the file.  If an error occurs in executing the contents of the
file, then the `source` command will return that error.

If a `return` command is invoked from within the file, the remainder of
the file will be skipped and the `source` command will return
normally with the result from the `return` command.

split
~~~~~
+*split* 'string ?splitChars?'+

Returns a list created by splitting +'string'+ at each character
that is in the +'splitChars'+ argument.

Each element of the result list will consist of the
characters from +'string'+ between instances of the
characters in +'splitChars'+.

Empty list elements will be generated if +'string'+ contains
adjacent characters in +'splitChars'+, or if the first or last
character of +'string'+ is in +'splitChars'+.

If +'splitChars'+ is an empty string then each character of
+'string'+ becomes a separate element of the result list.

+'splitChars'+ defaults to the standard white-space characters.
For example,

----
    split "comp.unix.misc" .
----

returns +'"comp unix misc"'+ and

----
    split "Hello world" {}
----

returns +'"H e l l o { } w o r l d"'+.

stackdump
~~~~~~~~~

+*stackdump* 'stacktrace'+

Creates a human readable representation of a stack trace.

stacktrace
~~~~~~~~~~

+*stacktrace*+

Returns a live stack trace as a list of +proc file line proc file line \...+.
Iteratively uses `info frame` to create the stack trace. This stack trace is in the
same form as produced by `catch` and `info stacktrace`

See also `stackdump`.

string
~~~~~~

+*string* 'option arg ?arg \...?'+

Perform one of several string operations, depending on +'option'+.
The legal options (which may be abbreviated) are:

+*string bytelength* 'string'+::
    Returns the length of the string in bytes. This will return
    the same value as `string length` if UTF-8 support is not enabled,
    or if the string is composed entirely of ASCII characters.
    See <<_utf_8_and_unicode,UTF-8 AND UNICODE>>.

+*string byterange* 'string first last'+::
    Like `string range` except works on bytes rather than characters.
    These commands are identical if UTF-8 support is not enabled.

+*string cat* '?string1 string2 \...?'+::
    Concatenates the given strings into a single string.

+*string compare ?-nocase?* ?*-length* 'len? string1 string2'+::
    Perform a character-by-character comparison of strings +'string1'+ and
    +'string2'+ in the same way as the C 'strcmp' procedure.  Return
    -1, 0, or 1, depending on whether +'string1'+ is lexicographically
    less than, equal to, or greater than +'string2'+. If +-length+
    is specified, then only the first +'len'+ characters are used
    in the comparison.  If +'len'+ is negative, it is ignored.
    Performs a case-insensitive comparison if +-nocase+ is specified.

+*string equal ?-nocase?* '?*-length* len?' 'string1 string2'+::
    Returns 1 if the strings are equal, or 0 otherwise. If +-length+
    is specified, then only the first +'len'+ characters are used
    in the comparison.  If +'len'+ is negative, it is ignored.
    Performs a case-insensitive comparison if +-nocase+ is specified.

+*string first* 'string1 string2 ?firstIndex?'+::
    Search +'string2'+ for a sequence of characters that exactly match
    the characters in +'string1'+.  If found, return the index of the
    first character in the first such match within +'string2'+.  If not
    found, return -1. If +'firstIndex'+ is specified, matching will start
    from +'firstIndex'+ of +'string1'+.
 ::
    See <<_string_and_list_index_specifications,STRING AND LIST INDEX SPECIFICATIONS>> for all allowed forms for +'firstIndex'+.

+*string index* 'string charIndex'+::
    Returns the +'charIndex'+'th character of the +'string'+
    argument.  A +'charIndex'+ of 0 corresponds to the first
    character of the string.
    If +'charIndex'+ is less than 0 or greater than
    or equal to the length of the string then an empty string is
    returned.
 ::
    See <<_string_and_list_index_specifications,STRING AND LIST INDEX SPECIFICATIONS>> for all allowed forms for +'charIndex'+.

+*string is* 'class' ?*-strict*? 'string'+::
    Returns 1 if +'string'+ is a valid member of the specified character
    class, otherwise returns 0. If +-strict+ is specified, then an
    empty string returns 0, otherwise an empty string will return 1
    on any class. The following character classes are recognized
    (the class name can be abbreviated):
  ::
  +alnum+;;  Any alphabet or digit character.
  +alpha+;;  Any alphabet character.
  +ascii+;;  Any character with a value less than 128 (those that are in the 7-bit ascii range).
  +boolean+;;  Any of the valid string formats for a boolean value in Tcl (0, false, no, off, 1, true, yes, on)
  +control+;; Any control character.
  +digit+;;  Any digit character.
  +double+;; Any of the valid forms for a double in Tcl, with optional surrounding whitespace.
             In case of under/overflow in the value, 0 is returned.
  +graph+;;  Any printing character, except space.
  +integer+;; Any of the valid string formats for an integer value in Tcl, with optional surrounding whitespace.
  +lower+;;  Any lower case alphabet character.
  +print+;;  Any printing character, including space.
  +punct+;;  Any punctuation character.
  +space+;;  Any space character.
  +upper+;;  Any upper case alphabet character.
  +xdigit+;; Any hexadecimal digit character ([0-9A-Fa-f]).
 ::
    Note that string classification does +'not'+ respect UTF-8. See <<_utf_8_and_unicode,UTF-8 AND UNICODE>>.
 ::
    Note that only +'lowercase'+ boolean values are recognized (Tcl accepts any case).

+*string last* 'string1 string2 ?lastIndex?'+::
    Search +'string2'+ for a sequence of characters that exactly match
    the characters in +'string1'+.  If found, return the index of the
    first character in the last such match within +'string2'+.  If there
    is no match, then return -1. If +'lastIndex'+ is specified, only characters
    up to +'lastIndex'+ of +'string2'+ will be considered in the match.
 ::
    See <<_string_and_list_index_specifications,STRING AND LIST INDEX SPECIFICATIONS>> for all allowed forms for +'lastIndex'+.

+*string length* 'string'+::
    Returns a decimal string giving the number of characters in +'string'+.
    If UTF-8 support is enabled, this may be different than the number of bytes.
    See <<_utf_8_and_unicode,UTF-8 AND UNICODE>>.

+*string map ?-nocase?* 'mapping string'+::
    Replaces substrings in +'string'+ based on the key-value pairs in
    +'mapping'+, which is a list of +key value key value \...+ as in the form
    returned by `array get`. Each instance of a key in the string will be
    replaced with its corresponding value.  If +-nocase+ is specified, then
    matching is done without regard to case differences. Both key and value may
    be multiple characters.  Replacement is done in an ordered manner, so the
    key appearing first in the list will be checked first, and so on. +'string'+ is
    only iterated over once, so earlier key replacements will have no affect for
    later key matches. For example,

----
      string map {abc 1 ab 2 a 3 1 0} 1abcaababcabababc
----

 ::
    will return the string +01321221+.
 ::
    Note that if an earlier key is a prefix of a later one, it will completely mask the later
    one.  So if the previous example is reordered like this,

----
      string map {1 0 ab 2 a 3 abc 1} 1abcaababcabababc
----

 ::
    it will return the string +02c322c222c+.

+*string match ?-nocase?* 'pattern string'+::
    See if +'pattern'+ matches +'string'+ according to
    <<_string_matching,STRING MATCHING>> rules
    ; return 1 if it does, 0
    if it doesn't. The match is performed in a case-insensitive manner if +-nocase+ is specified.

+*string range* 'string first last'+::
    Returns a range of consecutive characters from +'string'+, starting
    with the character whose index is +'first'+ and ending with the
    character whose index is +'last'+.  An index of 0 refers to the
    first character of the string.
 ::
    See <<_string_and_list_index_specifications,STRING AND LIST INDEX SPECIFICATIONS>> for all allowed forms for +'first'+ and +'last'+.
 ::
    If +'first'+ is less than zero then it is treated as if it were zero, and
    if +'last'+ is greater than or equal to the length of the string then
    it is treated as if it were +end+.  If +'first'+ is greater than
    +'last'+ then an empty string is returned.

+*string repeat* 'string count'+::
    Returns a new string consisting of +'string'+ repeated +'count'+ times.

+*string replace* 'string first last ?newstring?'+::
    Removes a range of consecutive characters from +'string'+, starting
    with the character whose index is +'first'+ and ending with the
    character whose index is +'last'+.  If +'newstring'+ is specified,
    then it is placed in the removed character range. If +'first'+ is
    less than zero then it is treated as if it were zero, and if +'last'+
    is greater than or equal to the length of the string then it is
    treated as if it were +end+. If +'first'+ is greater than +'last'+
    or the length of the initial string, or +'last'+ is less than 0,
    then the initial string is returned untouched.

+*string reverse* 'string'+::
    Returns a string that is the same length as +'string'+ but
    with its characters in the reverse order.

+*string tolower* 'string'+::
    Returns a value equal to +'string'+ except that all upper case
    letters have been converted to lower case.

+*string totitle* 'string'+::
    Returns a value equal to +'string'+ except that the first character
    is converted to title case (or upper case if there is no UTF-8 titlecase variant)
    and all remaining characters have been converted to lower case.

+*string toupper* 'string'+::
    Returns a value equal to +'string'+ except that all lower case
    letters have been converted to upper case.

+*string trim* 'string ?chars?'+::
    Returns a value equal to +'string'+ except that any leading
    or trailing characters from the set given by +'chars'+ are
    removed.
    If +'chars'+ is not specified then white space is removed
    (spaces, tabs, newlines, and carriage returns).

+*string trimleft* 'string ?chars?'+::
    Returns a value equal to +'string'+ except that any
    leading characters from the set given by +'chars'+ are
    removed.
    If +'chars'+ is not specified then white space is removed
    (spaces, tabs, newlines, and carriage returns).

+*string trimright* 'string ?chars?'+::
    Returns a value equal to +'string'+ except that any
    trailing characters from the set given by +'chars'+ are
    removed.
    If +'chars'+ is not specified then white space is removed
    (spaces, tabs, newlines, and carriage returns).
    Null characters are always removed.

subst
~~~~~
+*subst ?-nobackslashes? ?-nocommands? ?-novariables?* 'string'+

This command performs variable substitutions, command substitutions,
and backslash substitutions on its string argument and returns the
fully-substituted result. The substitutions are performed in exactly
the same way as for Tcl commands. As a result, the string argument
is actually substituted twice, once by the Tcl parser in the usual
fashion for Tcl commands, and again by the subst command.

If any of the +-nobackslashes+, +-nocommands+, or +-novariables+ are
specified, then the corresponding substitutions are not performed.
For example, if +-nocommands+ is specified, no command substitution
is performed: open and close brackets are treated as ordinary
characters with no special interpretation.

*Note*: when it performs its substitutions, subst does not give any
special treatment to double quotes or curly braces. For example,
the following script returns +xyz \{44\}+, not +xyz \{$a\}+.

----
    set a 44
    subst {xyz {$a}}
----


switch
~~~~~~
+*switch* '?options? string pattern body ?pattern body \...?'+

+*switch* '?options? string {pattern body ?pattern body \...?}'+

The `switch` command matches its string argument against each of
the pattern arguments in order. As soon as it finds a pattern that
matches string it evaluates the following body and returns the
result of that evaluation. If the last pattern argument is default
then it matches anything. If no pattern argument matches string and
no default is given, then the `switch` command returns an empty string.
If the initial arguments to switch start with - then they are treated
as options. The following options are currently supported:

    +-exact+::
        Use exact matching when comparing string to a
        pattern. This is the default.

    +-glob+::
        When matching string to the patterns, use glob-style
        <<_string_matching,STRING MATCHING>> rules.

    +-regexp+::
        When matching string to the patterns, use
        <<_regular_expressions,REGULAR EXPRESSIONS>> rules.

    +-command 'commandname'+::
        When matching string to the patterns, use the given command, which
        must be a single word. The command is invoked as
        'commandname pattern string', or 'commandname -nocase pattern string'
        and must return 1 if matched, or 0 if not.

    +--+::
        Marks the end of options. The argument following
        this one will be treated as string even if it starts
        with a +-+.

Two syntaxes are provided for the pattern and body arguments. The
first uses a separate argument for each of the patterns and commands;
this form is convenient if substitutions are desired on some of the
patterns or commands. The second form places all of the patterns
and commands together into a single argument; the argument must
have proper list structure, with the elements of the list being the
patterns and commands. The second form makes it easy to construct
multi-line `switch` commands, since the braces around the whole list
make it unnecessary to include a backslash at the end of each line.
Since the pattern arguments are in braces in the second form, no
command or variable substitutions are performed on them; this makes
the behaviour of the second form different than the first form in
some cases.

If a body is specified as +-+ it means that the body for the next
pattern should also be used as the body for this pattern (if the
next pattern also has a body of +-+ then the body after that is
used, and so on). This feature makes it possible to share a single
body among several patterns.

Below are some examples of `switch` commands:

----
    switch abc a - b {format 1} abc {format 2} default {format 3}
----

will return 2,

----
    switch -regexp aaab {
           ^a.*b$ -
           b {format 1}
           a* {format 2}
           default {format 3}
    }
----

will return 1, and

----
    switch xyz {
           a -
           b {format 1}
           a* {format 2}
           default {format 3}
    }
----

will return 3.

tailcall
~~~~~~~~
+*tailcall* 'cmd ?arg\...?'+

The `tailcall` command provides an optimised way of invoking a command whilst replacing
the current call frame. This is similar to 'exec' in Bourne Shell.

The following are identical except the first immediately replaces the current call frame.

----
  tailcall a b c
----

----
  return [uplevel 1 [list a b c]]
----

`tailcall` is useful as a dispatch mechanism:

----
  proc a {cmd args} {
    tailcall sub_$cmd {*}$args
  }
  proc sub_cmd1 ...
  proc sub_cmd2 ...
----

tell
~~~~
+*tell* 'fileId'+

+'fileId' *tell*+

Returns a decimal string giving the current access position in
+'fileId'+.

+'fileId'+ must have been the return value from a previous call to
`open`, or it may be +stdin+, +stdout+, or +stderr+ to refer to one
of the standard I/O channels.

throw
~~~~~
+*throw* 'code ?msg?'+

This command throws an exception (return) code along with an optional message.
This command is mostly for convenient usage with `try`.

The command +throw break+ is equivalent to +break+.
The command +throw 20 message+ can be caught with an +on 20 \...+ clause to `try`.

time
~~~~
+*time* 'command ?count?'+

This command will call the Tcl interpreter +'count'+
times to execute +'command'+ (or once if +'count'+ isn't
specified).  It will then return a string of the form

----
    503 microseconds per iteration
----

which indicates the average amount of time required per iteration,
in microseconds.

Time is measured in elapsed time, not CPU time.

try
~~~
+*try* '?catchopts? tryscript' ?*on* 'returncodes {?resultvar? ?optsvar?} handlerscript \...'? ?*finally* 'finalscript'?+

The `try` command is provided as a convenience for exception handling.

This interpeter first evaluates +'tryscript'+ under the effect of the catch
options +'catchopts'+ (e.g. +-signal -noexit --+, see `catch`).

It then evaluates the script for the first matching 'on' handler
(there many be zero or more) based on the return code from the `try`
section. For example a normal +JIM_ERR+ error will be matched by
an 'on error' handler.

Finally, any +'finalscript'+ is evaluated.

The result of this command is the result of +'tryscript'+, except in the
case where an exception occurs in a matching 'on' handler script or the 'finally' script,
in which case the result is this new exception.

The specified +'returncodes'+ is a list of return codes either as names ('ok', 'error', 'break', etc.)
or as integers.

If +'resultvar'+ and +'optsvar'+ are specified, they are set as for `catch` before evaluating
the matching handler.

For example:

----
    set f [open input]
    try -signal {
        process $f
    } on {continue break} {} {
        error "Unexpected break/continue"
    } on error {msg opts} {
        puts "Dealing with error"
        return {*}$opts $msg
    } on signal sig {
        puts "Got signal: $sig"
    } finally {
        $f close
    }
----

If break, continue or error are raised, they are dealt with by the matching
handler.

In any case, the file will be closed via the 'finally' clause.

See also `throw`, `catch`, `return`, `error`.

unknown
~~~~~~~
+*unknown* 'cmdName ?arg arg ...?'+

This command doesn't actually exist as part of Tcl, but Tcl will
invoke it if it does exist.

If the Tcl interpreter encounters a command name for which there
is not a defined command, then Tcl checks for the existence of
a command named `unknown`.

If there is no such command, then the interpreter returns an
error.

If the `unknown` command exists, then it is invoked with
arguments consisting of the fully-substituted name and arguments
for the original non-existent command.

The `unknown` command typically does things like searching
through library directories for a command procedure with the name
+'cmdName'+, or expanding abbreviated command names to full-length,
or automatically executing unknown commands as UNIX sub-processes.

In some cases (such as expanding abbreviations) `unknown` will
change the original command slightly and then (re-)execute it.
The result of the `unknown` command is used as the result for
the original non-existent command.

unset
~~~~~
+*unset ?-nocomplain? ?--?* '?name name ...?'+

Remove variables.
Each +'name'+ is a variable name, specified in any of the
ways acceptable to the `set` command.

If a +'name'+ refers to an element of an array, then that
element is removed without affecting the rest of the array.

If a +'name'+ consists of an array name with no parenthesized
index, then the entire array is deleted.

The `unset` command returns an empty string as result.

An error occurs if any of the variables doesn't exist, unless '-nocomplain'
is specified. The '--' argument may be specified to stop option processing
in case the variable name may be '-nocomplain'.

upcall
~~~~~~~
+*upcall* 'command ?args ...?'+

May be used from within a proc defined as `local` `proc` in order to call
the previous, hidden version of the same command.

If there is no previous definition of the command, an error is returned.

uplevel
~~~~~~~
+*uplevel* '?level? command ?command ...?'+

All of the +'command'+ arguments are concatenated as if they had
been passed to `concat`; the result is then evaluated in the
variable context indicated by +'level'+.  `uplevel` returns
the result of that evaluation.  If +'level'+ is an integer, then
it gives a distance (up the procedure calling stack) to move before
executing the command.  If +'level'+ consists of +\#+ followed by
a number then the number gives an absolute level number.  If +'level'+
is omitted then it defaults to +1+.  +'level'+ cannot be
defaulted if the first +'command'+ argument starts with a digit or +#+.

For example, suppose that procedure 'a' was invoked
from top-level, and that it called 'b', and that 'b' called 'c'.
Suppose that 'c' invokes the `uplevel` command.  If +'level'+
is +1+ or +#2+  or omitted, then the command will be executed
in the variable context of 'b'.  If +'level'+ is +2+ or +#1+
then the command will be executed in the variable context of 'a'.

If +'level'+ is '3' or +#0+ then the command will be executed
at top-level (only global variables will be visible).
The `uplevel` command causes the invoking procedure to disappear
from the procedure calling stack while the command is being executed.
In the above example, suppose 'c' invokes the command

----
    uplevel 1 {set x 43; d}
----

where 'd' is another Tcl procedure.  The `set` command will
modify the variable 'x' in 'b's context, and 'd' will execute
at level 3, as if called from 'b'.  If it in turn executes
the command

----
    uplevel {set x 42}
----

then the `set` command will modify the same variable 'x' in 'b's
context:  the procedure 'c' does not appear to be on the call stack
when 'd' is executing.  The command `info level` may
be used to obtain the level of the current procedure.

`uplevel` makes it possible to implement new control
constructs as Tcl procedures (for example, `uplevel` could
be used to implement the `while` construct as a Tcl procedure).

upvar
~~~~~
+*upvar* '?level? otherVar myVar ?otherVar myVar ...?'+

This command arranges for one or more local variables in the current
procedure to refer to variables in an enclosing procedure call or
to global variables.

+'level'+ may have any of the forms permitted for the `uplevel`
command, and may be omitted if the first letter of the first +'otherVar'+
isn't +#+ or a digit (it defaults to '1').

For each +'otherVar'+ argument, `upvar` makes the variable
by that name in the procedure frame given by +'level'+ (or at
global level, if +'level'+ is +#0+) accessible
in the current procedure by the name given in the corresponding
+'myVar'+ argument.

The variable named by +'otherVar'+ need not exist at the time of the
call;  it will be created the first time +'myVar'+ is referenced, just like
an ordinary variable.

`upvar` may only be invoked from within procedures.

`upvar` returns an empty string.

The `upvar` command simplifies the implementation of call-by-name
procedure calling and also makes it easier to build new control constructs
as Tcl procedures.
For example, consider the following procedure:

----
    proc add2 name {
        upvar $name x
        set x [expr $x+2]
    }
----

'add2' is invoked with an argument giving the name of a variable,
and it adds two to the value of that variable.
Although 'add2' could have been implemented using `uplevel`
instead of `upvar`, `upvar` makes it simpler for 'add2'
to access the variable in the caller's procedure frame.

wait
~~~~
+*wait*+

+*wait -nohang* 'pid'+

With no arguments, cleans up any processes started by `exec ... &` that have completed
(reaps zombie processes).

With one or two arguments, waits for a process by id, either returned by `exec ... &`
or by `os.fork` (if supported).

Waits for the process to complete, unless +-nohang+ is specified, in which case returns
immediately if the process is still running.

Returns a list of 3 elements.

+{NONE x x}+ if the process does not exist or has already been waited for, or
if -nohang is specified, and the process is still alive.

+{CHILDSTATUS <pid> <exit-status>}+ if the process exited normally.

+{CHILDKILLED <pid> <signal>}+ if the process terminated on a signal.

+{CHILDSUSP <pid> none}+ if the process terminated for some other reason.

Note that on platforms supporting waitpid(2), +pid+ can also be given special values such
as 0 or -1. See waitpid(2) for more detail.

while
~~~~~
+*while* 'test body'+

The +'while'+ command evaluates +'test'+ as an expression
(in the same way that `expr` evaluates its argument).
The value of the expression must be numeric; if it is non-zero
then +'body'+ is executed by passing it to the Tcl interpreter.

Once +'body'+ has been executed then +'test'+ is evaluated
again, and the process repeats until eventually +'test'+
evaluates to a zero numeric value.  `continue`
commands may be executed inside +'body'+ to terminate the current
iteration of the loop, and `break`
commands may be executed inside +'body'+ to cause immediate
termination of the `while` command.

The `while` command always returns an empty string.

xtrace
~~~~~~
+*xtrace* 'command'+

Install an execution trace callback command. This is useful for implementing a debugger
or tracing tool. On each command invocation, the given command is invoked as:

----
    command proc|cmd filename line result command arglist
----

+'proc'+ or +'cmd'+ indicates whether a command or a proc body is being executed.
+'filename'+ and +'line'+ indicate the location where the command was invoked.
+'result'+ is the current interpreter result (from the previous command).
+'command'+ and +'arglist'+ indicate the command being executed.

While the callback is executing, any further execution traces are temporarily disabled.
If the callback returns +JIM_OK+ or +JIM_RETURN+, the execution trace is reinstalled. Otherwise
the execution trace is removed.

If +*xtrace*+ is called with an empty argument (""), any existing callback is removed.

OPTIONAL-EXTENSIONS
-------------------

The following extensions may or may not be available depending upon
what options were selected when Jim Tcl was built.


[[cmd_1]]
posix: os.fork, os.gethostname, os.getids, os.uptime
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+*os.fork*+::
    Invokes 'fork(2)' and returns the result.

+*os.gethostname*+::
    Invokes 'gethostname(3)' and returns the result.

+*os.getids*+::
    Returns the various user/group ids for the current process.

----
    . os.getids
    uid 1000 euid 1000 gid 100 egid 100
----

+*os.uptime*+::
    Returns the number of seconds since system boot. See description of 'uptime' in 'sysinfo(2)'.

ANSI I/O (aio) and EVENTLOOP API
--------------------------------
Jim provides an alternative object-based API for I/O.

See `open` and `socket` for commands which return an I/O handle.

aio
~~~
+$handle *accept* ?addrvar?+::
    Server socket only: Accept a connection and return stream.
    If +'addrvar'+ is specified, the address of the connected client is stored
    in the named variable in the form 'addr:port' for IP sockets or 'path' for Unix domain sockets.
    See `socket` for details.

+$handle *buffering none|line|full*+::
    Sets the buffering mode of the stream.

+$handle *close ?r(ead)|w(rite)|-nodelete?*+::
    Closes the stream.
    The +'read'+ and +'write'+ arguments perform a "half-close" on a socket. See the 'shutdown(2)' man page.
    The +'-nodelete'+ option is applicable only for Unix domain sockets. It closes the socket
    but does not delete the bound path (e.g. after `os.fork`).


+$handle *copyto* 'tofd ?size?'+::
    Copy bytes to the file descriptor +'tofd'+. If +'size'+ is specified, at most
    that many bytes will be copied. Otherwise copying continues until the end
    of the input file. Returns the number of bytes actually copied.

+$handle *eof*+::
    Returns 1 if stream is at eof

+$handle *filename*+::
    Returns the original filename associated with the handle.
    Handles returned by `socket` give the socket type instead of a filename.

+$handle *flush*+::
    Flush the stream

+$handle *gets* '?var?'+::
    Read one line and return it or store it in the var

+$handle *isatty*+::
    Returns 1 if the stream is a tty device.

+$handle *lock ?-wait?*+::
    Apply a POSIX lock to the open file associated with the handle using
    'fcntl(F_SETLK)', or 'fcntl(F_SETLKW)' to wait for the lock to be available if +'-wait'+
    is specified.
    The handle must be open for write access.
    Returns 1 if the lock was successfully obtained, 0 otherwise.
    An error occurs if the handle is not suitable for locking (e.g.
    if it is not open for write)

+$handle *ndelay ?0|1?*+::
    Set O_NDELAY (if arg). Returns current/new setting.
    Note that in general ANSI I/O interacts badly with non-blocking I/O.
    Use with care.

+$handle *peername*+::
    Returns the remote address or path of the connected socket. See 'getpeername(2)'.

+$handle *puts ?-nonewline?* 'str'+::
    Write the string, with newline unless -nonewline

+$handle *read ?-nonewline|-pending*|len?'+::
    Read and return bytes from the stream. To eof if no len. See `read`.

+$handle *recvfrom* 'maxlen ?addrvar?'+::
    Receives a message from the handle via recvfrom(2) and returns it.
    At most +'maxlen'+ bytes are read. If +'addrvar'+ is specified, the sending address
    of the message is stored in the named variable in the form 'addr:port' for IP sockets
    or 'path' for Unix domain sockets. See `socket` for details.

+$handle *seek* 'offset' *?start|current|end?*+::
    Seeks in the stream (default 'current')

+$handle *sendto* 'str ?address'+::
    Sends the string, +'str'+, to the given address (host:port or path) via the socket using 'sendto(2)'.
    This is intended for udp/dgram sockets and may give an error or behave in unintended
    ways for other handle types.
    Returns the number of bytes written.

+$handle *sockname*+::
    Returns the bound address or path of the socket. See 'getsockname(2)'.

+$handle *sockopt* '?name value?'+::
    With no arguments, returns a dictionary of socket options currently set for the handle
    (will be empty for a non-socket). With +'name'+ and +'value'+, sets the socket option
    to the given value. Currently supports the following boolean socket options:
    +broadcast, debug, keepalive, nosigpipe, oobinline, tcp_nodelay+, and the following
    integer socket options: +sndbuf, rcvbuf+

+$handle *sync*+::
    Flush the stream, then 'fsync(2)' to commit any changes to storage.
    Only available on platforms that support 'fsync(2)'.

+$handle *tell*+::
    Returns the current seek position

+$handle *tty* ?settings?+::
    If no arguments are given, returns a dictionary containing the tty settings for the stream.
    If arguments are given, they must either be a dictionary, or +setting value \...+
    Abbreviations are supported for both settings and values, so the following is acceptable:
    +$f tty parity e input c out raw+.
    Only available on platforms that support 'termios(3)'. Supported settings are:

    +*baud* 'rate'+;;
        Baud rate. e.g. 115200

    +*data 5|6|7|8*+;;
        Number of data bits

    +*stop 1|2*+;;
        Number of stop bits

    +*parity even|odd|none*+;;
        Parity setting

    +*handshake xonxoff|rtscts|none*+;;
        Handshaking type

    +*input raw|cooked*+;;
        Input character processing. In raw mode, the usual key sequences such as ^C do
        not generate signals.

    +*output raw|cooked*+;;
        Output character processing. Typically CR -> CRNL is disabled in raw mode.

    +*echo 0|1*+;;
        Disable or enable echo on input. Note that this is a set-only value.
        Setting +input+ to +raw+ or +cooked+ will overwrite this setting.

    +*vmin* 'numchars'+;;
        Minimum number of characters to read.

    +*vtime* 'time'+;;
        Timeout for noncanonical read (units of 0.1 seconds)

+$handle *ssl* ?*-server* 'cert ?key?'|*-sni* 'servername'?+::
    Upgrades the stream to a SSL/TLS session and returns the handle.
    If +-server+ is specified, either both the certificate and private key files
    must be specified, or a single file must be specified containing both.
    If +-server+ is not specified, the connection is a client connection. In this case
    +-sni+ may be specified if required to set the Server Name Indication.

+$handle *unlock*+::
    Release a POSIX lock previously acquired by `aio lock`.

+$handle *verify*+::
    Verifies the certificate of a SSL/TLS stream peer

+*load_ssl_certs* 'dir'+::
    Loads SSL/TLS CA certificates for use during verification

fconfigure
~~~~~~~~~~
+*fconfigure* 'handle' *?-blocking 0|1? ?-buffering noneline|full? ?-translation* 'mode'?+::
    For compatibility with Tcl, a limited form of the `fconfigure`
    command is supported.
    * `fconfigure ... -blocking` maps to `aio ndelay`
    * `fconfigure ... -buffering` maps to `aio buffering`
    * `fconfigure ... -translation` is accepted but ignored

[[cmd_2]]
eventloop: after, vwait, update
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The following commands allow a script to be invoked when the given condition occurs.
If no script is given, returns the current script. If the given script is the empty, the
handler is removed.

+$handle *readable* '?readable-script?'+::
    Sets or returns the script for when the socket is readable.

+$handle *writable* '?writable-script?'+::
    Sets or returns the script for when the socket is writable.

+$handle *onexception* '?exception-script?'+::
    Sets or returns the script for when oob data received.

For compatibility with 'Tcl', these may be prefixed with `fileevent`.  e.g.

 ::
    +fileevent $handle *readable* '\...'+

Time-based execution is also available via the eventloop API.

+*after* 'ms'+::
    Sleeps for the given number of milliseconds. No events are
    processed during this time.

+*after* 'ms'|*idle* 'script ?script \...?'+::
    The scripts are concatenated and executed after the given
    number of milliseconds have elapsed.  If 'idle' is specified,
    the script will run the next time the event loop is processed
    with `vwait` or `update`. The script is only run once and
    then removed.  Returns an event id.

+*after cancel* 'id|command'+::
    Cancels an `after` event with the given event id or matching
    command (script).  Returns the number of milliseconds
    remaining until the event would have fired.  Returns the
    empty string if no matching event is found.

+*after info* '?id?'+::
    If +'id'+ is not given, returns a list of current `after`
    events.  If +'id'+ is given, returns a list containing the
    associated script and either 'timer' or 'idle' to indicated
    the type of the event. An error occurs if +'id'+ does not
    match an event.

+*vwait* 'variable'+::
    A call to `vwait` enters the eventloop. `vwait` processes
    events until the named (global) variable changes or all
    event handlers are removed. The variable need not exist
    beforehand.  If there are no event handlers defined, `vwait`
    returns immediately.

+*update ?idletasks?*+::
    A call to `update` enters the eventloop to process expired events, but
    no new events. If 'idletasks' is specified, only expired time events are handled,
    not file events.
    Returns once handlers have been run for all expired events.

Scripts are executed at the global scope. If an error occurs during a handler script,
an attempt is made to call (the user-defined command) `bgerror` with the details of the error.
If the `bgerror` command does not exist, the error message details are printed to stderr instead.

If a file event handler script generates an error, the handler is automatically removed
to prevent infinite errors. (A time event handler is always removed after execution).

+*bgerror* 'msg'+::
    Called when an event handler script generates an error. Note that the normal command resolution
    rules are used for bgerror. First the name is resolved in the current namespace, then in the
    global scope.

socket
~~~~~~
Various socket types may be created.

+*socket unix* 'path'+::
    A unix domain socket client connected to 'path'

+*socket unix.server* 'path'+::
    A unix domain socket server listening on 'path'

+*socket unix.dgram* '?path?'+::
    A unix domain socket datagram client, optionally connected to 'path'

+*socket unix.dgram.server* 'path'+::
    A unix domain socket datagram server server listening on 'path'

+*socket ?-ipv6? stream* 'addr:port'+::
    A TCP socket client. (See the forms for +'addr'+ below)

+*socket ?-ipv6? stream.server* '?addr:?port'+::
    A TCP socket server (+'addr'+ defaults to +0.0.0.0+ for IPv4 or +[::]+ for IPv6).

+*socket ?-ipv6? dgram* ?'addr:port'?+::
    A UDP socket client. If the address is not specified,
    the client socket will be unbound and 'sendto' must be used
    to indicated the destination.

+*socket ?-ipv6? dgram.server* 'addr:port'+::
    A UDP socket server.

+*socket pipe*+::
    A synonym for `pipe`

+*socket pair*+::
    A socketpair (see socketpair(2)). Like `pipe`, this command returns
    a list of two channels: {s1 s2}. These channels are both readable and writable.

+*socket pty*+::
    A pseudo-tty pair (see openpty(3)). Like `pipe`, this command returns
    a list of two channels: {master slave}. These channels are both readable and writable.

This command creates a socket connected (client) or bound (server) to the given
address.

The returned value is channel and may generally be used with the various file I/O
commands (gets, puts, read, etc.), either as object-based syntax or Tcl-compatible syntax.

----
    . set f [socket stream www.google.com:80]
    aio.sockstream1
    . $f puts -nonewline "GET / HTTP/1.0\r\n\r\n"
    . $f gets
    HTTP/1.0 302 Found
    . $f close
----

Server sockets, however support only 'accept', which is most useful in conjunction with
the EVENTLOOP API.

----
    set f [socket stream.server 80]
    $f readable {
        set client [$f accept]
        $client gets $buf
        ...
        $client puts -nonewline "HTTP/1.1 404 Not found\r\n"
        $client close
    }
    vwait done
----

The address, +'addr'+, can be given in one of the following forms:

1. For IPv4 socket types, an IPv4 address such as 192.168.1.1
2. For IPv6 socket types, an IPv6 address such as [fe80::1234] or [::]
3. A hostname

Note that on many systems, listening on an IPv6 address such as [::] will
also accept requests via IPv4.

Where a hostname is specified, the +'first'+ returned address is used
which matches the socket type is used.

An unconnected dgram socket (either 'dgram' or 'unix.dgram') must use
`sendto` to specify the destination address.

The path for Unix domain sockets is automatically removed when the socket
is closed. Use `close -nodelete` in the rare case where this behaviour
should be avoided (e.g. after `os.fork`).

syslog
~~~~~~
+*syslog* '?options? ?priority? message'+

This  command sends message to system syslog facility with given
priority. Valid priorities are:

    emerg, alert, crit, err, error, warning, notice, info, debug

If a message is specified, but no priority is specified, then a
priority of info is used.

By default, facility user is used and the value of global tcl variable
argv0 is used as ident string. However, any of the following options
may be specified before priority to control these parameters:

+*-facility* 'value'+::
    Use specified facility instead of user. The following
    values for facility are recognized:

    authpriv, cron, daemon, kernel, lpr, mail, news, syslog, user,
    uucp, local0-local7

+*-ident* 'string'+::
    Use given string instead of argv0 variable for ident string.

+*-options* 'integer'+::
    Set syslog options such as +LOG_CONS+, +LOG_NDELAY+. You should
    use numeric values of those from your system syslog.h file,
    because I haven't got time to implement yet another hash
    table.

pack: pack, unpack
~~~~~~~~~~~~~~~~~~
The optional 'pack' extension provides commands to encode and decode binary strings.

+*pack* 'varName value' *-intle|-intbe|-floatle|-floatbe|-str* 'bitwidth ?bitoffset?'+::
    Packs the binary representation of +'value'+ into the variable
    +'varName'+. The value is packed according to the given type
    (integer/floating point/string, big-endian/little-endian), width and bit offset.
    The variable is created if necessary (like `append`).
    The variable is expanded if necessary.

+*unpack* 'binvalue' *-intbe|-intle|-uintbe|-uintle|-floatbe|-floatle|-str* 'bitpos bitwidth'+::
    Unpacks bits from +'binvalue'+ at bit position +'bitpos'+ and with +'bitwidth'+.
    Interprets the value according to the type (integer/floating point/string, big-endian/little-endian
    and signed/unsigned) and returns it. For integer types, +'bitwidth'+
    may be up to the size of a Jim Tcl integer (typically 64 bits). For floating point types,
    +'bitwidth'+ may be 32 bits (for single precision numbers) or 64 bits (for double precision).
    For the string type, both the width and the offset must be on a byte boundary (multiple of 8). Attempting to
    access outside the length of the value will return 0 for integer types, 0.0 for floating point types
    or the empty string for the string type.

zlib
~~~~
The optional 'zlib' extension provides a Tcl-compatible subset of the `zlib` command.

+*crc32* 'data' '?startValue?'+::
    Returns the CRC32 checksum of a buffer. Optionally, an initial value may be specified; this is most useful
    for calculating the checksum of chunked data read from a stream (for instance, a pipe).

+*deflate* 'string' '?level?'+::
    Compresses a buffer and outputs a raw, Deflate-compressed stream. Optionally, a compression level (1-9) may
    be specified to choose the desired speed vs. compression rate ratio.

+*inflate* 'data' '?bufferSize?'+::
    Decompresses a raw, Deflate-compressed stream. When the uncompressed data size is known and specified, memory
    allocation is more efficient. Otherwise, decompression is chunked and therefore slower.

+*gzip* 'string' '?-level level?'+::
    Compresses a buffer and adds a gzip header.

+*gunzip* 'data' '?-buffersize size?'+::
    Decompresses a gzip-compressed buffer. Decompression is chunked, with a default, small buffer size of 64K
    which guarantees lower memory footprint at the cost of speed. It is recommended to use a bigger size, on
    systems without a severe memory constraint.

binary
~~~~~~
The optional, pure-Tcl 'binary' extension provides the Tcl-compatible `binary scan` and `binary format`
commands based on the low-level `pack` and `unpack` commands.

See the Tcl documentation at: http://www.tcl.tk/man/tcl8.5/TclCmd/binary.htm

Note that 'binary format' with f/r/R specifiers (single-precision float) uses the value of Infinity
in case of overflow.

oo: class, super
~~~~~~~~~~~~~~~~
The optional, pure-Tcl 'oo' extension provides object-oriented (OO) support for Jim Tcl.

See the online documentation (http://jim.tcl.tk/index.html/doc/www/www/documentation/oo/) for more details.

+*class* 'classname ?baseclasses? classvars'+::
    Create a new class, +'classname'+, with the given dictionary
    (+'classvars'+) as class variables. These are the initial variables
    which all newly created objects of this class are initialised with.
    If a list of baseclasses is given, methods and instance variables
    are inherited.

+*super* 'method ?args \...?'+::
    From within a method, invokes the given method on the base class.
    Note that this will only call the last baseclass given.

tree
~~~~
The optional, pure-Tcl 'tree' extension implements an OO, general purpose tree structure
similar to that provided by tcllib ::struct::tree (http://core.tcl.tk/tcllib/doc/trunk/embedded/www/tcllib/files/modules/struct/struct_tree.html)

A tree is a collection of nodes, where each node (except the root node) has a single parent
and zero or more child nodes (ordered), as well as zero or more attribute/value pairs.

+*tree*+::
    Creates and returns a new tree object with a single node named "root".
    All operations on the tree are invoked through this object.

+$tree *destroy*+::
    Destroy the tree and all it's nodes. (Note that the tree will also
    be automatically garbage collected once it goes out of scope).

+$tree *set* 'nodename key value'+::
    Set the value for the given attribute key.

+$tree *lappend* 'nodename key value \...'+::
    Append to the (list) value(s) for the given attribute key, or set if not yet set.

+$tree *keyexists* 'nodename key'+::
    Returns 1 if the given attribute key exists.

+$tree *get* 'nodename key'+::
    Returns the value associated with the given attribute key.

+$tree *getall* 'nodename'+::
    Returns the entire attribute dictionary associated with the given key.

+$tree *depth* 'nodename'+::
    Returns the depth of the given node. The depth of "root" is 0.

+$tree *parent* 'nodename'+::
    Returns the node name of the parent node, or "" for the root node.

+$tree *numchildren* 'nodename'+::
    Returns the number of child nodes.

+$tree *children* 'nodename'+::
    Returns a list of the child nodes.

+$tree *next* 'nodename'+::
    Returns the next sibling node, or "" if none.

+$tree *insert* 'nodename ?index?'+::
    Add a new child node to the given node. The index is a list index
    such as +3+ or +end-2+. The default index is +end+.
    Returns the name of the newly added node.

+$tree *walk* 'nodename' *dfs|bfs* {'actionvar nodevar'} 'script'+::
    Walks the tree starting from the given node, either breadth first (+bfs+)
    depth first (+dfs+).
    The value +"enter"+ or +"exit"+ is stored in variable +'actionvar'+.
    The name of each node is stored in +'nodevar'+.
    The script is evaluated twice for each node, on entry and exit.

+$tree *dump*+::
    Dumps the tree contents to stdout

tcl::prefix
~~~~~~~~~~~
The optional tclprefix extension provides the Tcl8.6-compatible `tcl::prefix` command
(http://www.tcl.tk/man/tcl8.6/TclCmd/prefix.htm) for matching strings against a table
of possible values (typically commands or options).

+*tcl::prefix all* 'table string'+::
    Returns a list of all elements in +'table'+ that begin with the prefix +'string'+.

+*tcl::prefix longest* 'table string'+::
    Returns the longest common prefix of all elements in +'table'+ that begin with the prefix +'string'+.

+*tcl::prefix match* '?options? table string'+::
    If +'string'+ equals one element in +'table'+ or is a prefix to
    exactly one element, the matched element is returned. If not, the
    result depends on the +-error+ option.

    * +*-exact*+ Accept only exact matches.
    * +*-message* 'string'+ Use +'string'+ in the error message at a mismatch. Default is "option".
    * +*-error* 'options'+ The options are used when no match is found. If +'options'+ is
      empty, no error is generated and an empty string is returned.
      Otherwise the options are used as return options when
      generating the error message. The default corresponds to
      setting +-level 0+.

tcl::autocomplete
~~~~~~~~~~~~~~~~~
Scriptable command line completion is supported in the interactive shell, 'jimsh', through
the `tcl::autocomplete` callback. A simple implementation is provided, however this may
be replaced with a custom command instead if desired.

In the interactive shell, press <TAB> to activate command line completion.

+*tcl::autocomplete* 'commandline'+::
    This command is called with the current command line when the user presses <TAB>.
    The command should return a list of all possible command lines that match the current command line.
    For example if +*pr*+ is the current command line, the list +*{prefix proc}*+ may be returned.

history
~~~~~~~
The optional history extension provides script access to the command line editing
and history support available in 'jimsh'. See 'examples/jtclsh.tcl' for an example.
Note: if line editing support is not available, `history getline` acts like `gets` and
the remaining subcommands do nothing.

+*history load* 'filename'+::
    Load history from a (text) file. If the file does not exist or is not readable,
    it is ignored.

+*history getline* 'prompt ?varname?'+::
    Displays the given prompt and allows a line to be entered. Similarly to `gets`,
    if +'varname'+ is given, it receives the line and the length of the line is returned,
    or -1 on EOF. If +'varname'+ is not given, the line is returned directly.

+*history completion* 'command'+::
    Sets an autocompletion command (see `tcl::autocomplete`) that is active during `history getline`.
    If the command is empty, autocompletion is disabled.

+*history add* 'line'+::
    Adds the given line to the history buffer.

+*history keep* '?count?'+::
    Set or return the maximum history size. Defaults to 100.

+*history save* 'filename'+::
    Saves the current history buffer to the given file.

+*history show*+::
    Displays the current history buffer to standard output.

namespace
~~~~~~~~~
Provides namespace-related functions. See also: http://www.tcl.tk/man/tcl8.6/TclCmd/namespace.htm

+*namespace code* 'script'+::
    Captures the current namespace context for later execution of
    the script +'script'+. It returns a new script in which script has
    been wrapped in a +*namespace inscope*+ command.

+*namespace current*+::
    Returns the fully-qualified name for the current namespace.

+*namespace delete* '?namespace ...?'+::
    Deletes all commands and variables with the given namespace prefixes.

+*namespace eval* 'namespace arg ?arg...?'+::
    Activates a namespace called +'namespace'+ and evaluates some code in that context.

+*namespace origin* 'command'+::
    Returns the fully-qualified name of the original command to which the imported command +'command'+ refers.

+*namespace parent* ?namespace?+::
    Returns the fully-qualified name of the parent namespace for namespace +'namespace'+, if given, otherwise
    for the current namespace.

+*namespace qualifiers* 'string'+::
    Returns any leading namespace qualifiers for +'string'+

+*namespace tail* 'string'+::
    Returns the simple name at the end of a qualified string.

+*namespace upvar* 'namespace ?arg...?'+::
    This command arranges for zero or more local variables in the current procedure to refer to variables in +'namespace'+

+*namespace which* '?-command|-variable? name'+::
    Looks up +'name'+ as either a command (the default) or variable and returns its fully-qualified name.

interp
~~~~~~
The optional 'interp' command allows sub-interpreters to be created where commands may be run
independently (but synchronously) of the main interpreter.

+*interp*+::
    Creates and returns a new interpreter object (command).
    The created interpreter contains any built-in commands along with static extensions,
    but does not include any dynamically loaded commands (package require, load).
    These must be reloaded in the child interpreter if required.

+*$interp delete*+::
    Deletes the interpreter object.

+*$interp eval* 'script' ...+::
    Evaluates a script in the context for the child interpreter, in the same way as 'eval'.

+*$interp alias* 'alias childcmd parentcmd ?arg ...?'+::
    Similar to 'alias', but creates a command, +'childcmd'+, in the child interpreter that is an
    alias for +'parentcmd'+ in the parent interpreter, with the given, fixed arguments.
    The alias may be deleted in the child with 'rename'.

json::encode
~~~~~~~~~~~~

The Tcl -> JSON encoder is part of the optional 'json' package.

+*json::encode* 'value ?schema?'+::

Encode a Tcl value as JSON according to the schema (defaults to +'str'+). The following schema types are supported:
* 'str' - Tcl string -> JSON string
* 'num' - Tcl value -> bare numeric value or null
* 'bool' - Tcl boolean value -> true, false
* 'obj ?name subschema ...?' - Tcl dict -> JSON object. For each dict key matching 'name', the corresponding 'subschema'
is applied. The special name +'*'+ matches any keys not otherwise matched, otherwise the default +'str'+ is used.
* 'list ?subschema?' - Tcl list -> JSON array. The 'subschema' (default +'str'+) is applied for each element of the list/array.
* 'mixed ?subschema ...?' = Tcl list -> JSON array. Each 'subschema' is applied for the corresponding element of the list/array.
  ::
The following are examples:
----
    . json::encode {1 2 true false null 5.0} list
    [ "1", "2", "true", "false", "null", "5.0" ]
    . json::encode {1 2 true false null 5.0} {list num}
    [ 1, 2, true, false, null, 5.0 ]
    . json::encode {0 1 2 true false 5.0 off} {list bool}
    [ false, true, true, true, false, true, false ]
    . json::encode {a 1 b hello c {3 4}} obj
    { "a":"1", "b":"hello", "c":"3 4" }
    . json::encode {a 1 b hello c {3 4}} {obj a num c {list num}}
    { "a":1, "b":"hello", "c":[ 3, 4 ] }
    . json::encode {true true {abc def}} {mixed str num obj}
    [ "true", true, { "abc":"def" } ]
    . json::encode {a 1 b 3.0 c hello d null} {obj c str * num}
    { "a":1, "b":3.0, "c":"hello", "d":null }
----

json::decode
~~~~~~~~~~~~

The JSON -> Tcl decoder is part of the optional 'json' package.

+*json::decode* ?*-index*? ?*-null* 'string'? ?*-schema*? 'json-string'+::

Decodes the given JSON string (must be array or object) into a Tcl data structure. If '+-index+' is specified,
decodes JSON arrays as dictionaries with numeric keys. This makes it possible to retrieve data from nested
arrays and dictionaries with just '+dict get+'. With the option '+-schema+' returns a list of +'{data schema}'+
where the schema is compatible with `json::encode`. Otherwise just returns the data.
Decoding is as follows (with schema types listed in parentheses):
* object -> dict ('obj')
* array -> list ('mixed' or 'list')
* number -> as-is ('num')
* boolean -> as-is ('bool')
* string -> string ('str')
* null -> supplied null string or the default +'"null"'+ ('num')
 ::
 Note that an object decoded into a dict will return the keys in the same order as the original string.
----
    . json::decode {[1, 2]}
    {1 2}
    . json::decode -schema {[1, 2]}
    {1 2} {list num}
    . json::decode -schema {{"a":1, "b":2}}
    {a 1 b 2} {obj a num b num}
    . json::decode -schema {[1, 2, {a:"b", c:false}, "hello"]}
    {1 2 {a b c false} hello} {mixed num num {obj a str c bool} str}
    . json::decode -index {["foo", "bar"]}
    {0 foo 1 bar}
----

[[BuiltinVariables]]
BUILT-IN VARIABLES
------------------

The following global variables are created automatically
by the Tcl library.

+*env*+::
    This variable is set by Jim as an array
    whose elements are the environment variables for the process.
    Reading an element will return the value of the corresponding
    environment variable.
    This array is initialised at startup from the `env` command.
    It may be modified and will affect the environment passed to
    commands invoked with `exec`.

+*platform_tcl*+::
    This variable is set by Jim as an array containing information
    about the platform on which Jim was built. Currently this includes
    'os' and 'platform'.

+*auto_path*+::
    This variable contains a list of paths to search for packages.
    It defaults to a location based on where jim is installed
    (e.g. +/usr/local/lib/jim+), but may be changed by +jimsh+
    or the embedding application. Note that +jimsh+ will consider
    the environment variable +$JIMLIB+ to be a list of colon-separated
    list of paths to add to +*auto_path*+.

+*errorCode*+::
    This variable holds the value of the -errorcode return
    option set by the most recent error that occurred in this
    interpreter. This list value represents additional information
    about the error in a form that is easy to process with
    programs. The first element of the list identifies a general
    class of errors, and determines the format of the rest of
    the list. The following formats for -errorcode return options
    are used by the Tcl core; individual applications may define
    additional formats. Currently only `exec` sets this variable.
    Otherwise it will be +NONE+.

The following global variables are set by jimsh.

+*tcl_interactive*+::
    This variable is set to 1 if jimsh is started in interactive mode
    or 0 otherwise.

+*tcl_platform*+::
    This variable is set by Jim as an array containing information
    about the platform upon which Jim was built. The following is an
    example of the contents of this array.

----
    tcl_platform(byteOrder)     = littleEndian
    tcl_platform(engine)        = Jim
    tcl_platform(os)            = Darwin
    tcl_platform(platform)      = unix
    tcl_platform(pointerSize)   = 8
    tcl_platform(threaded)      = 0
    tcl_platform(wordSize)      = 8
    tcl_platform(pathSeparator) = :
----

+*argv0*+::
    If jimsh is invoked to run a script, this variable contains the name
    of the script.

+*argv*+::
    If jimsh is invoked to run a script, this variable contains a list
    of any arguments supplied to the script.

+*argc*+::
    If jimsh is invoked to run a script, this variable contains the number
    of arguments supplied to the script.

+*jim::argv0*+::
    The value of argv[0] when jimsh was invoked.

The following variables have special meaning to Jim Tcl:

+*jim::defer*+::
    If this variable is set, it is considered to be a list of scripts to evaluate
    when the current proc exits (local variables), or the interpreter exits (global variable).
    See `defer`.

+*history::multiline*+::
    If this variable is set to "1", interactive line editing operates in multiline mode.
    That is, long lines will wrap across multiple lines rather than scrolling within a
    single line.

CHANGES IN PREVIOUS RELEASES
----------------------------

=== In v0.74 ===

1. Numbers with leading zeros are treated as decimal, not octal
2. Add `aio isatty`
3. Add LFS (64 bit) support for `aio seek`, `aio tell`, `aio copyto`, `file copy`
4. `string compare` and `string equal` now support '-length'
5. `glob` now supports '-directory'

=== In v0.73 ===

1. Built-in regexp now support non-capturing parentheses: (?:...)
2. Add `string replace`
3. Add `string totitle`
4. Add `info statics`
5. Add +build-jim-ext+ for easy separate building of loadable modules (extensions)
6. `local` now works with any command, not just procs
7. Add `info alias` to access the target of an alias
8. UTF-8 encoding past the basic multilingual plane (BMP) is supported
9. Add `tcl::prefix`
10. Add `history`
11. Most extensions are now enabled by default
12. Add support for namespaces and the `namespace` command
13. Add `apply`

=== In v0.72 ===

1. procs now allow 'args' and optional parameters in any position
2. Add Tcl-compatible expr functions, `rand()`, `srand()` and `pow()`
3. Add support for the '-force' option to `file delete`
4. Better diagnostics when `source` fails to load a script with a missing quote or bracket
5. New +tcl_platform(pathSeparator)+
6. Add support settings the modification time with `file mtime`
7. `exec` is now fully supported on win32 (mingw32)
8. `file join`, `pwd`, `glob` etc. now work for mingw32
9. Line editing is now supported for the win32 console (mingw32)
10. Add `aio listen` command

=== In v0.71 ===

1. Allow 'args' to be renamed in procs
2. Add +$(...)+ shorthand syntax for expressions
3. Add automatic reference variables in procs with +&var+ syntax
4. Support +jimsh --version+
5. Additional variables in +tcl_platform()+
6. `local` procs now push existing commands and `upcall` can call them
7. Add `loop` command (TclX compatible)
8. Add `aio buffering` command
9. `info complete` can now return the missing character
10. `binary format` and `binary scan` are now (optionally) supported
11. Add `string byterange`
12. Built-in regexp now support non-greedy repetition (*?, +?, ??)


=== In v0.70 ===

1. +platform_tcl()+ settings are now automatically determined
2. Add aio `$handle filename`
3. Add `info channels`
4. The 'bio' extension is gone. Now `aio` supports 'copyto'.
5. Add `exists` command
6. Add the pure-Tcl 'oo' extension
7. The `exec` command now only uses vfork(), not fork()
8. Unit test framework is less verbose and more Tcl-compatible
9. Optional UTF-8 support
10. Optional built-in regexp engine for better Tcl compatibility and UTF-8 support
11. Command line editing in interactive mode, e.g. 'jimsh'

=== In v0.63 ===

1. `source` now checks that a script is complete (.i.e. not missing a brace)
2. 'info complete' now uses the real parser and so is 100% accurate
3. Better access to live stack frames with 'info frame', `stacktrace` and `stackdump`
4. `tailcall` no longer loses stack trace information
5. Add `alias` and `curry`
6. `lambda`, `alias` and `curry` are implemented via `tailcall` for efficiency
7. `local` allows procedures to be deleted automatically at the end of the current procedure
8. udp sockets are now supported for both clients and servers.
9. vfork-based exec is now working correctly
10. Add 'file tempfile'
11. Add 'socket pipe'
12. Enhance 'try ... on ... finally' to be more Tcl 8.6 compatible
13. It is now possible to `return` from within `try`
14. IPv6 support is now included
15. Add 'string is'
16. Event handlers works better if an error occurs. eof handler has been removed.
17. `exec` now sets $::errorCode, and catch sets opts(-errorcode) for exit status
18. Command pipelines via open "|..." are now supported
19. `pid` can now return pids of a command pipeline
20. Add 'info references'
21. Add support for 'after +'ms'+', 'after idle', 'after info', `update`
22. `exec` now sets environment based on $::env
23. Add 'dict keys'
24. Add support for 'lsort -index'

=== In v0.62 ===

1. Add support to `exec` for '>&', '>>&', '|&', '2>@1'
2. Fix `exec` error messages when special token (e.g. '>') is the last token
3. Fix `subst` handling of backslash escapes.
4. Allow abbreviated options for `subst`
5. Add support for `return`, `break`, `continue` in subst
6. Many `expr` bug fixes
7. Add support for functions in `expr` (e.g. int(), abs()), and also 'in', 'ni' list operations
8. The variable name argument to `regsub` is now optional
9. Add support for 'unset -nocomplain'
10. Add support for list commands: `lassign`, `lrepeat`
11. Fully-functional `lsearch` is now implemented
12. Add 'info nameofexecutable' and 'info returncodes'
13. Allow `catch` to determine what return codes are caught
14. Allow `incr` to increment an unset variable by first setting to 0
15. Allow 'args' and optional arguments to the left or required arguments in `proc`
16. Add 'file copy'
17. Add 'try ... finally' command


LICENCE
-------

 Copyright 2005 Salvatore Sanfilippo <antirez@invece.org>
 Copyright 2005 Clemens Hintze <c.hintze@gmx.net>
 Copyright 2005 patthoyts - Pat Thoyts <patthoyts@users.sf.net>
 Copyright 2008 oharboe - Oyvind Harboe - oyvind.harboe@zylin.com
 Copyright 2008 Andrew Lunn <andrew@lunn.ch>
 Copyright 2008 Duane Ellis <openocd@duaneellis.com>
 Copyright 2008 Uwe Klein <uklein@klein-messgeraete.de>
 Copyright 2009 Steve Bennett <steveb@workware.net.au>

[literal]
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions
 are met:
 1. Redistributions of source code must retain the above copyright
    notice, this list of conditions and the following disclaimer.
 2. Redistributions in binary form must reproduce the above
    copyright notice, this list of conditions and the following
    disclaimer in the documentation and/or other materials
    provided with the distribution.

 THIS SOFTWARE IS PROVIDED BY THE JIM TCL PROJECT ``AS IS'' AND ANY
 EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 JIM TCL PROJECT OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 The views and conclusions contained in the software and documentation
 are those of the authors and should not be interpreted as representing
 official policies, either expressed or implied, of the Jim Tcl Project.