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| -rw-r--r-- | doc/re_syntax.n | 74 |
1 files changed, 42 insertions, 32 deletions
diff --git a/doc/re_syntax.n b/doc/re_syntax.n index 63eb76c..4e018bc 100644 --- a/doc/re_syntax.n +++ b/doc/re_syntax.n @@ -5,7 +5,7 @@ '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" -'\" RCS: @(#) $Id: re_syntax.n,v 1.1 1999/06/24 21:15:13 jpeek Exp $ +'\" RCS: @(#) $Id: re_syntax.n,v 1.2 1999/07/13 02:07:37 jpeek Exp $ '\" .so man.macros .TH re_syntax n "8.1" Tcl "Tcl Built-In Commands" @@ -20,7 +20,6 @@ A \fIregular expression\fR describes strings of characters. It's a pattern that matches certain strings and doesn't match others. .SH "DIFFERENT FLAVORS OF REs" -.VS 8.1 Regular expressions (``RE''s), as defined by POSIX, come in two flavors: \fIextended\fR REs (``EREs'') and \fIbasic\fR REs (``BREs''). EREs are roughly those of the traditional \fIegrep\fR, while BREs are @@ -223,24 +222,23 @@ enclosed in stands for the sequence of characters of that collating element. The sequence is a single element of the bracket expression's list. -A bracket expression in a locale which has +A bracket expression in a locale that has multi-character collating elements can thus match more than one character. -Most insidiously, if -\fB^\fR -is used, -this can happen even if no multi-character collating -elements appear in the bracket expression! -If the collating sequence includes a -\fBch\fR -multi-character collating element, -then the RE -\fB[[.ch.]]*c\fR -matches the first five characters -of `\fBchchcc\fR', -and the RE -\fB[^c]b\fR -matches all of `\fBchb\fR'. +.VS 8.2 +So (insidiously), a bracket expression that starts with \fB^\fR +can match multi-character collating elements even if none of them +appear in the bracket expression! +(\fINote:\fR Tcl currently has no multi-character collating elements. +This information is only for illustration.) +.PP +For example, assume the collating sequence includes a \fBch\fR +multi-character collating element. +Then the RE \fB[[.ch.]]*c\fR (zero or more \fBch\fP's followed by \fBc\fP) +matches the first five characters of `\fBchchcc\fR'. +Also, the RE \fB[^c]b\fR matches all of `\fBchb\fR' +(because \fB[^c]\fR matches the multi-character \fBch\fR). +.VE 8.2 .PP Within a bracket expression, a collating element enclosed in \fB[=\fR @@ -261,6 +259,12 @@ and `\fB[o\o'o^']\fR'\& are all synonymous. An equivalence class may not be an endpoint of a range. +.VS 8.2 +(\fINote:\fR +Tcl currently implements only the Unicode locale. +It doesn't define any equivalence classes. +The examples above are just illustrations.) +.VE 8.2 .PP Within a bracket expression, the name of a \fIcharacter class\fR enclosed in @@ -271,7 +275,7 @@ stands for the list of all characters (not all collating elements!) belonging to that class. -Standard character classes are (*** CHECK THESE! ***): +Standard character classes are: .PP .RS .ne 5 @@ -283,15 +287,20 @@ Standard character classes are (*** CHECK THESE! ***): \fBdigit\fR A decimal digit. \fBxdigit\fR A hexadecimal digit. \fBalnum\fR An alphanumeric (letter or digit). +\fBprint\fR An alphanumeric (same as alnum). +\fBblank\fR A space or tab character. \fBspace\fR A character producing white space in displayed text. \fBpunct\fR A punctuation character. -\fBprint\fR A printing character. \fBgraph\fR A character with a visible representation. \fBcntrl\fR A control character. .fi .RE .PP -A locale may provide others. (*** NOT ANYMORE, TRUE? ***) +A locale may provide others. +.VS 8.2 +(Note that the current Tcl implementation has only one locale: +the Unicode locale.) +.VE 8.2 A character class may not be used as an endpoint of a range. .PP There are two special cases of bracket expressions: @@ -304,12 +313,11 @@ the beginning and end of a word respectively. '\" note, discussion of escapes below references this definition of word A word is defined as a sequence of word characters -which is neither preceded nor followed by +that is neither preceded nor followed by word characters. A word character is an \fIalnum\fR -character (as defined by -\fIctype\fR(3)) +character or an underscore (\fB_\fR). These special bracket expressions are deprecated; @@ -340,7 +348,7 @@ non-printing and otherwise inconvenient characters in REs: .RS 2 .TP 5 \fB\ea\fR -alert, aka bell, character, as in C +alert (bell) character, as in C .TP \fB\eb\fR backspace, as in C @@ -471,6 +479,10 @@ lose their outer brackets, and `\fB\eD\fR', `\fB\eS\fR', and `\fB\eW\fR'\& are illegal. +.VS 8.2 +(So, for example, \fB[a-c\ed]\fR is equivalent to \fB[a-c[:digit:]]\fR. +Also, \fB[a-c\eD]\fR, which is equivalent to \fB[a-c^[:digit:]]\fR, is illegal.) +.VE 8.2 .PP A constraint escape (AREs only) is a constraint, matching the empty string if specific conditions are met, @@ -491,7 +503,7 @@ matches only at the end of a word matches only at the beginning or end of a word .TP \fB\eY\fR -matches only at a point which is not the beginning or end of a word +matches only at a point that is not the beginning or end of a word .TP \fB\eZ\fR matches only at the end of the string @@ -634,10 +646,10 @@ white space and comments are illegal within multi-character symbols like the ARE `\fB(?:\fR' or the BRE `\fB\e(\fR' .RE .PP -Expanded-syntax -white-space characters are blank, tab, newline, etc. (any character -defined as \fIspace\fR by -\fIctype\fR(3)). +Expanded-syntax white-space characters are blank, tab, newline, and +.VS 8.2 +any character that belongs to the \fIspace\fR character class. +.VE 8.2 Exactly how a multi-line expanded-syntax RE can be entered interactively by a user, if at all, is application-specific; @@ -917,8 +929,6 @@ and respectively; no other escapes are available. -.VE 8.1 - .SH "SEE ALSO" RegExp(3), regexp(n), regsub(n), lsearch(n), switch(n), text(n) |