'\" '\" Copyright (c) 1993 The Regents of the University of California. '\" Copyright (c) 1994-1996 Sun Microsystems, Inc. '\" Copyright (c) 2023 Nathan Coulter '\" '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" .TH Tcl n "8.6" Tcl "Tcl Built-In Commands" .so man.macros .BS .SH NAME Tcl \- Tool Command Language .SH SYNOPSIS Summary of Tcl language syntax. .BE .SH DESCRIPTION .PP The following rules define the syntax and semantics of the Tcl language: . .IP "[1] \fBScript.\fR" A script is composed of zero or more commands delimited by semi-colons or newlines. .IP "[2] \fBCommand.\fR" A command is composed of zero or more words delimited by whitespace. The replacement for a substitution is included verbatim in the word. For example, a space in the replacement is included in the word rather than becoming a delimiter, and \fI\\\\\fR becomes a single backslash in the word. Each word is processed from left to right and each substitution is performed as soon as it is complete. For example, the command .RS .PP .CS set y [set x 0][incr x][incr x] .CE .PP is composed of three words, and sets the value of \fIy\fR to \fI012\fR. .PP If hash .PQ # is the first character of what would otherwise be the first word of a command, all characters up to the next newline are ignored. .RE . .IP "[3] \fBBraced word.\fR" If a word is enclosed in braces .PQ { and .PQ } "" , the braces are removed and the enclosed characters become the word. No substitutions are performed. Nested pairs of braces may occur within the word. A brace preceded by an odd number of backslashes is not considered part of a pair, and neither brace nor the backslashes are removed from the word. . .IP "[4] \fBQuoted word.\fR" If a word is enclosed in double quotes .PQ \N'34' , the double quotes are removed and the enclosed characters become the word. Substitutions are performed. . .IP "[5] \fBList.\fR" A list has the form of a single command. Newline is whitespace, and semicolon has no special interpretation. There is no script evaluation so there is no argument expansion, variable substitution, or command substitution: Dollar-sign and open bracket have no special interpretation, and what would be argument expansion in a script is invalid in a list. . .IP "[6] \fBArgument expansion.\fR" If .QW {*} prefixes a word, it is removed. After any remaining enclosing braces or quotes are processed and applicable substitutions performed, the word, which must be a list, is removed from the command, and in its place each word in the list becomes an additional word in the command. For example, .CS cmd a {*}{b [c]} d {*}{$e f {g h}} .CE is equivalent to .CS cmd a b {[c]} d {$e} f {g h} . .CE . .IP "[7] \fBEvaluation.\fR" To evaluate a script, an interpreter evaluates each successive command. The first word identifies a procedure, and the remaining words are passed to that procedure for further evaluation. The procedure interprets each argument in its own way, e.g. as an integer, variable name, list, mathematical expression, script, or in some other arbitrary way. The result of the last command is the result of the script. . .IP "[8] \fBCommand substitution.\fR" Each pair of brackets .PQ [ and .PQ ] "" encloses a script and is replaced by the result of that script. .IP "[9] \fBVariable substitution.\fR" Each of the following forms begins with dollar sign .PQ $ and is replaced by the value of the identified variable. \fIname\fR names the variable and is composed of ASCII letters (\fBA\fR\(en\fBZ\fR and \fBa\fR\(en\fBz\fR), digits (\fB0\fR\(en\fB9\fR), underscores, or namespace delimiters (two or more colons). \fIindex\fR is the name of an individual variable within an array variable, and may be empty. .RS .TP 15 \fB$\fIname\fR . \fIname\fR may not be empty. .TP 15 \fB$\fIname\fB(\fIindex\fB)\fR . \fIname\fR may be empty. Substitutions are performed on \fIindex\fR. .TP 15 \fB${\fIname\fB}\fR \fIname\fR may be empty. .TP 15 \fB${\fIname(index)\fB}\fR . \fIname\fR may be empty. No substitutions are performed. .RE Variables that are not accessible through one of the forms above may be accessed through other mechanisms, e.g. the \fBset\fR command. .IP "[10] \fBBackslash substitution.\fR" Each backslash .PQ \e that is not part of one of the forms listed below is removed, and the next character is included in the word verbatim, which allows the inclusion of characters that would normally be interpreted, namely whitespace, braces, brackets, double quote, dollar sign, and backslash. The following sequences are replaced as described: .RS .RS .RS .TP 7 \e\fBa\fR Audible alert (bell) (U+7). .TP 7 \e\fBb\fR Backspace (U+8). .TP 7 \e\fBf\fR Form feed (U+C). .TP 7 \e\fBn\fR Newline (U+A). .TP 7 \e\fBr\fR Carriage-return (U+D). .TP 7 \e\fBt\fR Tab (U+9). .TP 7 \e\fBv\fR Vertical tab (U+B). .TP 7 \e\fB\fIwhiteSpace\fR . Newline preceded by an odd number of backslashes, along with the consecutive spaces and tabs that immediately follow it, is replaced by a single space. Because this happens before the command is split into words, it occurs even within braced words, and if the resulting space may subsequently be treated as a word delimiter. .TP 7 \e\e Backslash .PQ \e "" . .TP 7 \e\fIooo\fR . Up to three octal digits form an eight-bit value for a Unicode character in the range \fI0\fR\(en\fI377\fR, i.e. U+0\(enU+FF. Only the digits that result in a number in this range are consumed. .TP 7 \e\fBx\fIhh\fR . Up to two hexadecimal digits form an eight-bit value for a Unicode character in the range \fI0\fR\(en\fIFF\fR. .TP 7 \e\fBu\fIhhhh\fR . Up to four hexadecimal digits form a 16-bit value for a Unicode character in the range \fI0\fR\(en\fIFFFF\fR. .TP 7 \e\fBU\fIhhhhhhhh\fR . Up to eight hexadecimal digits form a 21-bit value for a Unicode character in the range \fI0\fR\(en\fI10FFFF\fR. Only the digits that result in a number in this range are consumed. .RE .RE .PP .RE . .SH KEYWORDS backslash, command, comment, script, substitution, variable '\" Local Variables: '\" mode: nroff '\" fill-column: 78 '\" End: