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Diffstat (limited to 'doc/re_syntax.n')
| -rw-r--r-- | doc/re_syntax.n | 204 |
1 files changed, 123 insertions, 81 deletions
diff --git a/doc/re_syntax.n b/doc/re_syntax.n index eebda51..f1eabbc 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 1.15 2007/11/14 11:13:32 dkf Exp $ +'\" RCS: @(#) $Id: re_syntax.n,v 1.16 2007/11/15 12:02:56 dkf Exp $ '\" .so man.macros .TH re_syntax n "8.1" Tcl "Tcl Built-In Commands" @@ -50,7 +50,7 @@ A branch is zero or more \fIconstraints\fR or \fIquantified atoms\fR, concatenated. It matches a match for the first, followed by a match for the second, etc; an empty branch matches the empty string. -.PP +.SS QUANTIFIERS A quantified atom is an \fIatom\fR possibly followed by a single \fIquantifier\fR. Without a quantifier, it matches a single match for the atom. @@ -93,7 +93,7 @@ of matches (see \fBMATCHING\fR) The forms using \fB{\fR and \fB}\fR are known as \fIbound\fRs. The numbers \fIm\fR and \fIn\fR are unsigned decimal integers with permissible values from 0 to 255 inclusive. -.PP +.SS ATOMS An atom is one of: .RS 2 .IP \fB(\fIre\fB)\fR 6 @@ -128,7 +128,7 @@ when followed by a digit, it is the beginning of a \fIbound\fR (see above) where \fIx\fR is a single character with no other significance, matches that character. .RE -.PP +.SS CONSTRAINTS A \fIconstraint\fR matches an empty string when specific conditions are met. A constraint may not be followed by a quantifier. The simple constraints are as follows; some more constraints are described @@ -163,7 +163,7 @@ An RE may not end with A \fIbracket expression\fR is a list of characters enclosed in .QW \fB[\|]\fR . It normally matches any single character from the list -(but see below). If the list begins with +(but see below). If the list begins with .QW \fB^\fR , it matches any single character (but see below) \fInot\fR from the rest of the list. @@ -171,22 +171,25 @@ rest of the list. If two characters in the list are separated by .QW \fB\-\fR , this is shorthand for the full \fIrange\fR of characters between those two -(inclusive) in the collating sequence, e.g. \fB[0\-9]\fR in Unicode -matches any conventional decimal digit. Two ranges may not share an -endpoint, so e.g. \fBa\-c\-e\fR is illegal. Ranges in Tcl always use the +(inclusive) in the collating sequence, e.g. +.QW \fB[0\-9]\fR +in Unicode matches any conventional decimal digit. Two ranges may not share an +endpoint, so e.g. +.QW \fBa\-c\-e\fR +is illegal. Ranges in Tcl always use the Unicode collating sequence, but other programs may use other collating sequences and this can be a source of incompatability between programs. .PP To include a literal \fB]\fR or \fB\-\fR in the list, the simplest method is to enclose it in \fB[.\fR and \fB.]\fR to make it a -collating element (see below). Alternatively, make it the first +collating element (see below). Alternatively, make it the first character (following a possible .QW \fB^\fR ), or (AREs only) precede it with .QW \fB\e\fR . Alternatively, for .QW \fB\-\fR , -make it the last character, or the second endpoint of a range. To use +make it the last character, or the second endpoint of a range. To use a literal \fB\-\fR as the first endpoint of a range, make it a collating element or (AREs only) precede it with .QW \fB\e\fR . @@ -194,48 +197,7 @@ With the exception of these, some combinations using \fB[\fR (see next paragraphs), and escapes, all other special characters lose their special significance within a bracket expression. -.PP -Within a bracket expression, a collating element (a character, a -multi-character sequence that collates as if it were a single -character, or a collating-sequence name for either) enclosed in -\fB[.\fR and \fB.]\fR 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 that has -multi-character collating elements can thus match more than one -character. 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 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\fRs followed by \fBc\fR) matches the first five -characters of -.QW \fBchchcc\fR . -Also, the RE \fB[^c]b\fR matches all of -.QW \fBchb\fR -(because \fB[^c]\fR matches the multi-character \fBch\fR). -.PP -Within a bracket expression, a collating element enclosed in \fB[=\fR -and \fB=]\fR is an equivalence class, standing for the sequences of -characters of all collating elements equivalent to that one, including -itself. (If there are no other equivalent collating elements, the -treatment is as if the enclosing delimiters were -.QW \fB[.\fR \& -and -.QW \fB.]\fR .) -For example, if \fBo\fR and \fB\N'244'\fR are the members of an -equivalence class, then -.QW \fB[[=o=]]\fR , -.QW \fB[[=\N'244'=]]\fR , -and -.QW \fB[o\N'244']\fR \& -are all synonymous. An equivalence class may -not be an endpoint of a range. (\fINote:\fR Tcl implements only the -Unicode locale. It does not define any equivalence classes. The -examples above are just illustrations.) -.PP +.SS "CHARACTER CLASSES" Within a bracket expression, the name of a \fIcharacter class\fR enclosed in \fB[:\fR and \fB:]\fR stands for the list of all characters (not all collating elements!) belonging to that class. @@ -265,30 +227,94 @@ A character with a visible representation (includes both alnum and punct). .IP \fBcntrl\fR 8 A control character. .PP -A locale may provide others. (Note that the current Tcl -implementation has only one locale: the Unicode locale.) A character -class may not be used as an endpoint of a range. +A locale may provide others. A character class may not be used as an endpoint +of a range. +.RS .PP +(\fINote:\fR the current Tcl implementation has only one locale, the Unicode +locale, which supports exactly the above classes.) +.RE +.SS "BRACKETED CONSTRAINTS" There are two special cases of bracket expressions: the bracket -expressions \fB[[:<:]]\fR and \fB[[:>:]]\fR are constraints, matching -empty strings at 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 that is neither -preceded nor followed by word characters. A word character is an -\fIalnum\fR character or an underscore (\fB_\fR). These special -bracket expressions are deprecated; users of AREs should use +expressions +.QW \fB[[:<:]]\fR +and +.QW \fB[[:>:]]\fR +are constraints, matching empty strings at 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 that is neither preceded +nor followed by word characters. A word character is an \fIalnum\fR character +or an underscore +.PQ \fB_\fR "" . +These special bracket expressions are deprecated; users of AREs should use constraint escapes instead (see below). +.SS "COLLATING ELEMENTS" +Within a bracket expression, a collating element (a character, a +multi-character sequence that collates as if it were a single +character, or a collating-sequence name for either) enclosed in +\fB[.\fR and \fB.]\fR 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 that has +multi-character collating elements can thus match more than one +character. 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! +.RS +.PP +(\fINote:\fR Tcl has no multi-character collating elements. This information +is only for illustration.) +.RE +.PP +For example, assume the collating sequence includes a \fBch\fR multi-character +collating element. Then the RE +.QW \fB[[.ch.]]*c\fR +(zero or more +.QW \fBch\fRs +followed by +.QW \fBc\fR ) +matches the first five characters of +.QW \fBchchcc\fR . +Also, the RE +.QW \fB[^c]b\fR +matches all of +.QW \fBchb\fR +(because +.QW \fB[^c]\fR +matches the multi-character +.QW \fBch\fR ). +.SS "EQUIVALENCE CLASSES" +Within a bracket expression, a collating element enclosed in \fB[=\fR +and \fB=]\fR is an equivalence class, standing for the sequences of +characters of all collating elements equivalent to that one, including +itself. (If there are no other equivalent collating elements, the +treatment is as if the enclosing delimiters were +.QW \fB[.\fR \& +and +.QW \fB.]\fR .) +For example, if \fBo\fR and \fB\N'244'\fR are the members of an +equivalence class, then +.QW \fB[[=o=]]\fR , +.QW \fB[[=\N'244'=]]\fR , +and +.QW \fB[o\N'244']\fR \& +are all synonymous. An equivalence class may not be an endpoint of a range. +.RS +.PP +(\fINote:\fR Tcl implements only the Unicode locale. It does not define any +equivalence classes. The examples above are just illustrations.) +.RE .SH ESCAPES Escapes (AREs only), which begin with a \fB\e\fR followed by an alphanumeric character, come in several varieties: character entry, -class shorthands, constraint escapes, and back references. A \fB\e\fR +class shorthands, constraint escapes, and back references. A \fB\e\fR followed by an alphanumeric character but not constituting a valid -escape is illegal in AREs. In EREs, there are no escapes: outside a +escape is illegal in AREs. In EREs, there are no escapes: outside a bracket expression, a \fB\e\fR followed by an alphanumeric character merely stands for that character as an ordinary character, and inside -a bracket expression, \fB\e\fR is an ordinary character. (The latter +a bracket expression, \fB\e\fR is an ordinary character. (The latter is the one actual incompatibility between EREs and AREs.) -.PP +.SS "CHARACTER-ENTRY ESCAPES" Character-entry escapes (AREs only) exist to make it easier to specify non-printing and otherwise inconvenient characters in REs: .RS 2 @@ -380,13 +406,13 @@ Octal digits are .PP The character-entry escapes are always taken as ordinary characters. For example, \fB\e135\fR is \fB]\fR in Unicode, but \fB\e135\fR does -not terminate a bracket expression. Beware, however, that some +not terminate a bracket expression. Beware, however, that some applications (e.g., C compilers and the Tcl interpreter if the regular expression is not quoted with braces) interpret such sequences themselves before the regular-expression package gets to see them, which may require doubling (quadrupling, etc.) the .QW \fB\e\fR . -.PP +.SS "CLASS-SHORTHAND ESCAPES" Class-shorthand escapes (AREs only) provide shorthands for certain commonly-used character classes: .RS 2 @@ -426,10 +452,16 @@ lose their outer brackets, and .QW \fB\eS\fR , and .QW \fB\eW\fR \& -are illegal. (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.) -.PP +are illegal. (So, for example, +.QW \fB[a-c\ed]\fR +is equivalent to +.QW \fB[a-c[:digit:]]\fR . +Also, +.QW \fB[a-c\eD]\fR , +which is equivalent to +.QW \fB[a-c^[:digit:]]\fR , +is illegal.) +.SS "CONSTRAINT ESCAPES" A constraint escape (AREs only) is a constraint, matching the empty string if specific conditions are met, written as an escape: .RS 2 @@ -474,13 +506,20 @@ closing capturing parentheses seen so far) a \fIback reference\fR, see below .RE .PP -A word is defined as in the specification of \fB[[:<:]]\fR and -\fB[[:>:]]\fR above. Constraint escapes are illegal within bracket -expressions. -.PP +A word is defined as in the specification of +.QW \fB[[:<:]]\fR +and +.QW \fB[[:>:]]\fR +above. Constraint escapes are illegal within bracket expressions. +.SS "BACK REFERENCES" A back reference (AREs only) matches the same string matched by the parenthesized subexpression specified by the number, so that (e.g.) -\fB([bc])\e1\fR matches \fBbb\fR or \fBcc\fR but not +.QW \fB([bc])\e1\fR +matches +.QW \fBbb\fR +or +.QW \fBcc\fR +but not .QW \fBbc\fR . The subexpression must entirely precede the back reference in the RE. Subexpressions are numbered in the order of their leading parentheses. @@ -488,9 +527,9 @@ Non-capturing parentheses do not define subexpressions. .PP There is an inherent historical ambiguity between octal character-entry escapes and back references, which is resolved by -heuristics, as hinted at above. A leading zero always indicates an -octal escape. A single non-zero digit, not followed by another digit, -is always taken as a back reference. A multi-digit sequence not +heuristics, as hinted at above. A leading zero always indicates an +octal escape. A single non-zero digit, not followed by another digit, +is always taken as a back reference. A multi-digit sequence not starting with a zero is taken as a back reference if it comes after a suitable subexpression (i.e. the number is in the legal range for a back reference), and otherwise is taken as octal. @@ -762,7 +801,10 @@ it appears at the beginning of the RE or the beginning of a parenthesized subexpression (after a possible leading .QW \fB^\fR ). Finally, single-digit back references are available, and \fB\e<\fR and -\fB\e>\fR are synonyms for \fB[[:<:]]\fR and \fB[[:>:]]\fR +\fB\e>\fR are synonyms for +.QW \fB[[:<:]]\fR +and +.QW \fB[[:>:]]\fR respectively; no other escapes are available. .SH "SEE ALSO" RegExp(3), regexp(n), regsub(n), lsearch(n), switch(n), text(n) |