latex/wx/re_syntax.tex

4 \section{Syntax of the builtin regular expression library}\label{wxresyn}
6 A {\it regular expression} describes strings of characters. It's a
13 \subsection{Different Flavors of REs}\label{differentflavors}
15 \helpref{Syntax of the builtin regular expression library}{wxresyn}
19 of the traditional {\it egrep}, while BREs are roughly those of the traditional
26 of AREs. Features of AREs that are not present in EREs will be indicated.
30 \helpref{Syntax of the builtin regular expression library}{wxresyn}
34 (not quite all) of the Perl5 extensions (thanks, Henry!).  Much of the description
35 of regular expressions below is copied verbatim from his manual entry.
38 any of the branches.
49 \twocolitem{{\bf *}}{a sequence of 0 or more matches of the atom}
50 \twocolitem{{\bf +}}{a sequence of 1 or more matches of the atom}
51 \twocolitem{{\bf ?}}{a sequence of 0 or 1 matches of the atom}
52 \twocolitem{{\bf \{m\}}}{a sequence of exactly {\it m} matches of the atom}
53 \twocolitem{{\bf \{m,\}}}{a sequence of {\it m} or more matches of the atom}
54 \twocolitem{{\bf \{m,n\}}}{a sequence of {\it m} through {\it n} (inclusive)
55 matches of the atom; {\it m} may not exceed {\it n}}
58 smallest number rather than the largest number of matches (see \helpref{Matching}{wxresynmatching})}
63 An atom is one of:
69 does no reporting (a ``non-capturing'' set of parentheses)}
73 \twocolitem{{\bf $[chars]$}}{a {\it bracket expression}, matching any one of the {\it chars}
83 a digit, it is the beginning of a {\it bound} (see above)}
93 \twocolitem{{\bf \caret}}{matches at the beginning of a line}
94 \twocolitem{{\bf \$}}{matches at the end of a line}
108 \helpref{Syntax of the builtin regular expression library}{wxresyn}
111 of characters enclosed in `{\bf $[]$}'. It normally matches any single character from
113 character (but see below) {\it not} from the rest of the list.
116 in the list are separated by `{\bf -}', this is shorthand for the full {\it range} of
127 it the last character, or the second endpoint of a range. To use a literal
128  {\bf -} as the first endpoint of a range, make it a collating element or (AREs
129 only) precede it with `{\bf $\backslash$}'. With the exception of these, some combinations using
137 sequence of characters of that collating element.
141 the name of a character. For example, the following are both identical
146 %The sequence is a single element of the bracket
150 %elements even if none of them appear in the bracket expression! ({\it Note:}
156 % {\bf ch}'s followed by {\bf c}) matches the first five characters of `{\bf chchcc}'. Also, the
157 %RE {\bf $[^c]b$} matches all of `{\bf chb}' (because {\bf $[^c]$} matches the multi-character {\bf ch}).
160 is an equivalence class, standing for the sequences of characters of all
165 %and {\bf \caret} are the members of an
168 An equivalence class may not be an endpoint of a range.
176  {\it X} can either be a single character literal or the name of a character,
180 the name of a {\it character class} enclosed in {\bf $[:$} and {\bf $:]$} stands for the list
181 of all characters (not all collating elements!) belonging to that class.
201 A character class may not be used as an endpoint of a range.
208 There are two special cases of bracket expressions:
210 strings at the beginning and end of a word respectively.  A word is defined
211 as a sequence of word characters that is neither preceded nor followed
213 ({\bf \_}). These special bracket expressions are deprecated; users of AREs should
218 \helpref{Syntax of the builtin regular expression library}{wxresyn}
239 are multiple levels of backslash processing}
241 the character whose low-order 5 bits are the same as those of {\it X}, and whose
257  {\it hhh} is any sequence of hexadecimal digits) the character whose hexadecimal
303 \twocolitem{{\bf $\backslash$A}}{matches only at the beginning of the string
306 \twocolitem{{\bf $\backslash$m}}{matches only at the beginning of a word}
307 \twocolitem{{\bf $\backslash$M}}{matches only at the end of a word}
308 \twocolitem{{\bf $\backslash$y}}{matches only at the beginning or end of a word}
309 \twocolitem{{\bf $\backslash$Y}}{matches only at a point that is not the beginning or end of
311 \twocolitem{{\bf $\backslash$Z}}{matches only at the end of the string
317 and the decimal value {\it mnn} is not greater than the number of closing capturing
322 as in the specification of {\bf $[[:$<$:]]$} and {\bf $[[:$>$:]]$} above. Constraint escapes are
330 in the order of their leading parentheses. Non-capturing parentheses do not
344 \helpref{Syntax of the builtin regular expression library}{wxresyn}
349 Normally the flavor of RE being used is specified by application-dependent
350 means. However, this can be overridden by a {\it director}. If an RE of any flavor
351 begins with `{\bf ***:}', the rest of the RE is an ARE. If an RE of any flavor begins
352 with `{\bf ***=}', the rest of the RE is taken to be a literal string, with all
357 specifies options affecting the rest of the RE. These supplement, and can
362 \twocolitem{{\bf b}}{rest of RE is a BRE}
364 \twocolitem{{\bf e}}{rest of RE is an ERE}
369 \twocolitem{{\bf q}}{rest of RE
379 sequence. They are available only at the start of an ARE, and may not be
384 %in all flavors of RE with the {\bf -expanded} switch, or
387 all characters between a {\bf \#} and the following newline (or the end of the
405 this is not allowed between the characters of multi-character symbols like
409 {\it None} of these
416 \helpref{Syntax of the builtin regular expression library}{wxresyn}
419 one substring of a given string, the RE matches the one starting earliest
431 quantified atom in it which has a preference. An RE consisting of two or
447 of `{\bf abbbc}', {\bf (week$|$wee)(night$|$knights)}
448 matches all ten characters of `{\bf weeknights}', when {\bf (.*).*} is matched against
458 inside a bracket expression, all case counterparts of it are added to the
466 and end of string respectively. ARE {\bf $\backslash$A} and {\bf $\backslash$Z} continue to match beginning
467 or end of string {\it only}.
479 \helpref{Syntax of the builtin regular expression library}{wxresyn}
481 No particular limit is imposed on the length of REs. Programs
486 feature of AREs that is actually incompatible with POSIX EREs is that {\bf $\backslash$}
489 effects in POSIX EREs; the {\bf ***} syntax of directors likewise is outside
492 Many of the ARE extensions are
494 few Perl extensions are not present. Incompatibilities of note include `{\bf $\backslash$b}',
495 `{\bf $\backslash$B}', the lack of special treatment for a trailing newline, the addition of
502 quantifiers have changed since early beta-test versions of this package.
507 %(e.g., in pre-8.1 releases of Tcl),
508 implemented an early version of today's EREs. There are four incompatibilities between {\it regexp}'s
509 near-EREs (`RREs' for short) and AREs. In roughly increasing order of significance:
512 an error, while in RREs, it was just another way of writing the  alphanumeric.
516 \item {\bf \{} followed by a digit in an ARE is the beginning of
530 (The careful crafting of RREs to optimize the search order for fast matching
539 \helpref{Syntax of the builtin regular expression library}{wxresyn}
548 character except at the beginning of the RE or the beginning of a parenthesized
549 subexpression, {\bf \$} is an ordinary character except at the end of the RE or
550 the end of a parenthesized subexpression, and {\bf *} is an ordinary character
551 if it appears at the beginning of the RE or the beginning of a parenthesized
559 \helpref{Syntax of the builtin regular expression library}{wxresyn}