190 lines
6.9 KiB
Plaintext
190 lines
6.9 KiB
Plaintext
'\"
|
|
'\" Copyright (c) 1993 The Regents of the University of California.
|
|
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
|
|
'\"
|
|
'\" See the file "license.terms" for information on usage and redistribution
|
|
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
|
|
'\"
|
|
'\" SCCS: @(#) Tcl.n 1.127 96/03/25 20:08:20
|
|
'
|
|
.so man.macros
|
|
.TH Tcl n "" Tcl "Tcl Built-In Commands"
|
|
.BS
|
|
.SH NAME
|
|
Tcl \- Summary of Tcl language syntax.
|
|
.BE
|
|
|
|
.SH DESCRIPTION
|
|
.PP
|
|
The following rules define the syntax and semantics of the Tcl language:
|
|
.IP [1]
|
|
A Tcl script is a string containing one or more commands.
|
|
Semi-colons and newlines are command separators unless quoted as
|
|
described below.
|
|
Close brackets are command terminators during command substitution
|
|
(see below) unless quoted.
|
|
.IP [2]
|
|
A command is evaluated in two steps.
|
|
First, the Tcl interpreter breaks the command into \fIwords\fR
|
|
and performs substitutions as described below.
|
|
These substitutions are performed in the same way for all
|
|
commands.
|
|
The first word is used to locate a command procedure to
|
|
carry out the command, then all of the words of the command are
|
|
passed to the command procedure.
|
|
The command procedure is free to interpret each of its words
|
|
in any way it likes, such as an integer, variable name, list,
|
|
or Tcl script.
|
|
Different commands interpret their words differently.
|
|
.IP [3]
|
|
Words of a command are separated by white space (except for
|
|
newlines, which are command separators).
|
|
.IP [4]
|
|
If the first character of a word is double-quote (``"'') then
|
|
the word is terminated by the next double-quote character.
|
|
If semi-colons, close brackets, or white space characters
|
|
(including newlines) appear between the quotes then they are treated
|
|
as ordinary characters and included in the word.
|
|
Command substitution, variable substitution, and backslash substitution
|
|
are performed on the characters between the quotes as described below.
|
|
The double-quotes are not retained as part of the word.
|
|
.IP [5]
|
|
If the first character of a word is an open brace (``{'') then
|
|
the word is terminated by the matching close brace (``}'').
|
|
Braces nest within the word: for each additional open
|
|
brace there must be an additional close brace (however,
|
|
if an open brace or close brace within the word is
|
|
quoted with a backslash then it is not counted in locating the
|
|
matching close brace).
|
|
No substitutions are performed on the characters between the
|
|
braces except for backslash-newline substitutions described
|
|
below, nor do semi-colons, newlines, close brackets,
|
|
or white space receive any special interpretation.
|
|
The word will consist of exactly the characters between the
|
|
outer braces, not including the braces themselves.
|
|
.IP [6]
|
|
If a word contains an open bracket (``['') then Tcl performs
|
|
\fIcommand substitution\fR.
|
|
To do this it invokes the Tcl interpreter recursively to process
|
|
the characters following the open bracket as a Tcl script.
|
|
The script may contain any number of commands and must be terminated
|
|
by a close bracket (``]'').
|
|
The result of the script (i.e. the result of its last command) is
|
|
substituted into the word in place of the brackets and all of the
|
|
characters between them.
|
|
There may be any number of command substitutions in a single word.
|
|
Command substitution is not performed on words enclosed in braces.
|
|
.IP [7]
|
|
If a word contains a dollar-sign (``$'') then Tcl performs \fIvariable
|
|
substitution\fR: the dollar-sign and the following characters are
|
|
replaced in the word by the value of a variable.
|
|
Variable substitution may take any of the following forms:
|
|
.RS
|
|
.TP 15
|
|
\fB$\fIname\fR
|
|
\fIName\fR is the name of a scalar variable; the name is terminated
|
|
by any character that isn't a letter, digit, or underscore.
|
|
.TP 15
|
|
\fB$\fIname\fB(\fIindex\fB)\fR
|
|
\fIName\fR gives the name of an array variable and \fIindex\fR gives
|
|
the name of an element within that array.
|
|
\fIName\fR must contain only letters, digits, and underscores.
|
|
Command substitutions, variable substitutions, and backslash
|
|
substitutions are performed on the characters of \fIindex\fR.
|
|
.TP 15
|
|
\fB${\fIname\fB}\fR
|
|
\fIName\fR is the name of a scalar variable. It may contain any
|
|
characters whatsoever except for close braces.
|
|
.LP
|
|
There may be any number of variable substitutions in a single word.
|
|
Variable substitution is not performed on words enclosed in braces.
|
|
.RE
|
|
.IP [8]
|
|
If a backslash (``\e'') appears within a word then
|
|
\fIbackslash substitution\fR occurs.
|
|
.VS
|
|
In all cases but those described below the backslash is dropped and
|
|
the following character is treated as an ordinary
|
|
character and included in the word.
|
|
.VE
|
|
This allows characters such as double quotes, close brackets,
|
|
and dollar signs to be included in words without triggering
|
|
special processing.
|
|
The following table lists the backslash sequences that are
|
|
handled specially, along with the value that replaces each sequence.
|
|
.RS
|
|
.VS
|
|
.TP 6
|
|
\e\fBa\fR
|
|
Audible alert (bell) (0x7).
|
|
.VE
|
|
.TP 6
|
|
\e\fBb\fR
|
|
Backspace (0x8).
|
|
.TP 6
|
|
\e\fBf\fR
|
|
Form feed (0xc).
|
|
.TP 6
|
|
\e\fBn\fR
|
|
Newline (0xa).
|
|
.TP 6
|
|
\e\fBr\fR
|
|
Carriage-return (0xd).
|
|
.TP 6
|
|
\e\fBt\fR
|
|
Tab (0x9).
|
|
.TP 6
|
|
\e\fBv\fR
|
|
Vertical tab (0xb).
|
|
.TP 6
|
|
\e\fB<newline>\fIwhiteSpace\fR
|
|
.VS
|
|
A single space character replaces the backslash, newline, and all
|
|
spaces and tabs after the newline.
|
|
This backslash sequence is unique in that it is replaced in a separate
|
|
pre-pass before the command is actually parsed.
|
|
This means that it will be replaced even when it occurs between
|
|
braces, and the resulting space will be treated as a word separator
|
|
if it isn't in braces or quotes.
|
|
.VE
|
|
.TP 6
|
|
\e\e
|
|
Backslash (``\e'').
|
|
.TP 6
|
|
\e\fIooo\fR
|
|
The digits \fIooo\fR (one, two, or three of them) give the octal value of
|
|
the character.
|
|
.TP 6
|
|
\e\fBx\fIhh\fR
|
|
.VS
|
|
The hexadecimal digits \fIhh\fR give the hexadecimal value of
|
|
the character. Any number of digits may be present.
|
|
.VE
|
|
.LP
|
|
Backslash substitution is not performed on words enclosed in braces,
|
|
except for backslash-newline as described above.
|
|
.RE
|
|
.IP [9]
|
|
If a hash character (``#'') appears at a point where Tcl is
|
|
expecting the first character of the first word of a command,
|
|
then the hash character and the characters that follow it, up
|
|
through the next newline, are treated as a comment and ignored.
|
|
The comment character only has significance when it appears
|
|
at the beginning of a command.
|
|
.IP [10]
|
|
Each character is processed exactly once by the Tcl interpreter
|
|
as part of creating the words of a command.
|
|
For example, if variable substitution occurs then no further
|
|
substitutions are performed on the value of the variable; the
|
|
value is inserted into the word verbatim.
|
|
If command substitution occurs then the nested command is
|
|
processed entirely by the recursive call to the Tcl interpreter;
|
|
no substitutions are performed before making the recursive
|
|
call and no additional substitutions are performed on the result
|
|
of the nested script.
|
|
.IP [11]
|
|
Substitutions do not affect the word boundaries of a command.
|
|
For example, during variable substitution the entire value of
|
|
the variable becomes part of a single word, even if the variable's
|
|
value contains spaces.
|