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author | William Joye <wjoye@cfa.harvard.edu> | 2016-12-21 22:46:09 (GMT) |
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committer | William Joye <wjoye@cfa.harvard.edu> | 2016-12-21 22:46:09 (GMT) |
commit | 768f87f613cc9789fcf8073018fa02178c8c91df (patch) | |
tree | ec633f5608ef498bee52a5f42c12c49493ec8bf8 /tcl8.6/doc/Tcl.n | |
parent | 07e464099b99459d0a37757771791598ef3395d9 (diff) | |
parent | 05fa4c89f20e9769db0e6c0b429cef2590771ace (diff) | |
download | blt-768f87f613cc9789fcf8073018fa02178c8c91df.zip blt-768f87f613cc9789fcf8073018fa02178c8c91df.tar.gz blt-768f87f613cc9789fcf8073018fa02178c8c91df.tar.bz2 |
Merge commit '05fa4c89f20e9769db0e6c0b429cef2590771ace' as 'tcl8.6'
Diffstat (limited to 'tcl8.6/doc/Tcl.n')
-rw-r--r-- | tcl8.6/doc/Tcl.n | 275 |
1 files changed, 275 insertions, 0 deletions
diff --git a/tcl8.6/doc/Tcl.n b/tcl8.6/doc/Tcl.n new file mode 100644 index 0000000..fc3b477 --- /dev/null +++ b/tcl8.6/doc/Tcl.n @@ -0,0 +1,275 @@ +'\" +'\" 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. +'\" +.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] \fBCommands.\fR" +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] \fBEvaluation.\fR" +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. +Secondly, 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] \fBWords.\fR" +Words of a command are separated by white space (except for +newlines, which are command separators). +.IP "[4] \fBDouble quotes.\fR" +If the first character of a word is double-quote +.PQ \N'34' +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] \fBArgument expansion.\fR" +If a word starts with the string +.QW {*} +followed by a non-whitespace character, then the leading +.QW {*} +is removed and the rest of the word is parsed and substituted as any other +word. After substitution, the word is parsed as a list (without command or +variable substitutions; backslash substitutions are performed as is normal for +a list and individual internal words may be surrounded by either braces or +double-quote characters), and its words are added to the command being +substituted. For instance, +.QW "cmd a {*}{b [c]} d {*}{$e f {g h}}" +is equivalent to +.QW "cmd a b {[c]} d {$e} f {g h}" . +.IP "[6] \fBBraces.\fR" +If the first character of a word is an open brace +.PQ { +and rule [5] does not apply, then +the word is terminated by the matching close brace +.PQ } "" . +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 "[7] \fBCommand substitution.\fR" +If a word contains an open bracket +.PQ [ +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 +.PQ ] "" . +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 "[8] \fBVariable substitution.\fR" +If a word contains a dollar-sign +.PQ $ +followed by one of the forms +described below, 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 a sequence +of one or more characters that are a letter, digit, underscore, +or namespace separators (two or more colons). +Letters and digits are \fIonly\fR the standard ASCII ones (\fB0\fR\(en\fB9\fR, +\fBA\fR\(en\fBZ\fR and \fBa\fR\(en\fBz\fR). +.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, underscores, and +namespace separators, and may be an empty string. +Letters and digits are \fIonly\fR the standard ASCII ones (\fB0\fR\(en\fB9\fR, +\fBA\fR\(en\fBZ\fR and \fBa\fR\(en\fBz\fR). +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 or array element. It may contain +any characters whatsoever except for close braces. It indicates an array +element if \fIname\fR is in the form +.QW \fIarrayName\fB(\fIindex\fB)\fR +where \fIarrayName\fR does not contain any open parenthesis characters, +.QW \fB(\fR , +or close brace characters, +.QW \fB}\fR , +and \fIindex\fR can be any sequence of characters except for close brace +characters. No further +substitutions are performed during the parsing of \fIname\fR. +.PP +There may be any number of variable substitutions in a single word. +Variable substitution is not performed on words enclosed in braces. +.PP +Note that variables may contain character sequences other than those listed +above, but in that case other mechanisms must be used to access them (e.g., +via the \fBset\fR command's single-argument form). +.RE +.IP "[9] \fBBackslash substitution.\fR" +If a backslash +.PQ \e +appears within a word then \fIbackslash substitution\fR occurs. +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. +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 +.TP 7 +\e\fBa\fR +Audible alert (bell) (Unicode U+000007). +.TP 7 +\e\fBb\fR +Backspace (Unicode U+000008). +.TP 7 +\e\fBf\fR +Form feed (Unicode U+00000C). +.TP 7 +\e\fBn\fR +Newline (Unicode U+00000A). +.TP 7 +\e\fBr\fR +Carriage-return (Unicode U+00000D). +.TP 7 +\e\fBt\fR +Tab (Unicode U+000009). +.TP 7 +\e\fBv\fR +Vertical tab (Unicode U+00000B). +.TP 7 +\e\fB<newline>\fIwhiteSpace\fR +. +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 is not +in braces or quotes. +.TP 7 +\e\e +Backslash +.PQ \e "" . +.TP 7 +\e\fIooo\fR +. +The digits \fIooo\fR (one, two, or three of them) give a eight-bit octal +value for the Unicode character that will be inserted, in the range +\fI000\fR\(en\fI377\fR (i.e., the range U+000000\(enU+0000FF). +The parser will stop just before this range overflows, or when +the maximum of three digits is reached. The upper bits of the Unicode +character will be 0. +.TP 7 +\e\fBx\fIhh\fR +. +The hexadecimal digits \fIhh\fR (one or two of them) give an eight-bit +hexadecimal value for the Unicode character that will be inserted. The upper +bits of the Unicode character will be 0 (i.e., the character will be in the +range U+000000\(enU+0000FF). +.TP 7 +\e\fBu\fIhhhh\fR +. +The hexadecimal digits \fIhhhh\fR (one, two, three, or four of them) give a +sixteen-bit hexadecimal value for the Unicode character that will be +inserted. The upper bits of the Unicode character will be 0 (i.e., the +character will be in the range U+000000\(enU+00FFFF). +.TP 7 +\e\fBU\fIhhhhhhhh\fR +. +The hexadecimal digits \fIhhhhhhhh\fR (one up to eight of them) give a +twenty-one-bit hexadecimal value for the Unicode character that will be +inserted, in the range U+000000\(enU+10FFFF. The parser will stop just +before this range overflows, or when the maximum of eight digits +is reached. The upper bits of the Unicode character will be 0. +.RS +.PP +The range U+010000\(enU+10FFFD is reserved for the future. +.RE +.PP +Backslash substitution is not performed on words enclosed in braces, +except for backslash-newline as described above. +.RE +.IP "[10] \fBComments.\fR" +If a hash character +.PQ # +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 "[11] \fBOrder of substitution.\fR" +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. +.RS +.PP +Substitutions take place from left to right, and each substitution is +evaluated completely before attempting to evaluate the next. Thus, a +sequence like +.PP +.CS +set y [set x 0][incr x][incr x] +.CE +.PP +will always set the variable \fIy\fR to the value, \fI012\fR. +.RE +.IP "[12] \fBSubstitution and word boundaries.\fR" +Substitutions do not affect the word boundaries of a command, +except for argument expansion as specified in rule [5]. +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. +.SH KEYWORDS +backslash, command, comment, script, substitution, variable +'\" Local Variables: +'\" mode: nroff +'\" fill-column: 78 +'\" End: |