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author | rjohnson <rjohnson> | 1998-03-26 14:45:59 (GMT) |
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committer | rjohnson <rjohnson> | 1998-03-26 14:45:59 (GMT) |
commit | 2b5738da524e944cda39e24c0a87b745a43bd8c3 (patch) | |
tree | 6e8c9473978f6dab66c601e911721a7bd9d70b1b /doc/Tcl.n | |
parent | c6a259aeeca4814a97cf6694814c63e74e4e18fa (diff) | |
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diff --git a/doc/Tcl.n b/doc/Tcl.n new file mode 100644 index 0000000..610fe1b --- /dev/null +++ b/doc/Tcl.n @@ -0,0 +1,181 @@ +'\" +'\" 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 1.128 96/08/26 12:59:50 +' +.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. +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 6 +\e\fBa\fR +Audible alert (bell) (0x7). +.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 +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. +.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 +The hexadecimal digits \fIhh\fR give the hexadecimal value of +the character. Any number of digits may be present. +.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. |