+++ /dev/null
-.\" From Henry Spencer's regex package (as found in the apache
-.\" distribution). The package carries the following copyright:
-.\"
-.\" Copyright 1992, 1993, 1994 Henry Spencer. All rights reserved.
-.\" %%%LICENSE_START(MISC)
-.\" This software is not subject to any license of the American Telephone
-.\" and Telegraph Company or of the Regents of the University of California.
-.\"
-.\" Permission is granted to anyone to use this software for any purpose
-.\" on any computer system, and to alter it and redistribute it, subject
-.\" to the following restrictions:
-.\"
-.\" 1. The author is not responsible for the consequences of use of this
-.\" software, no matter how awful, even if they arise from flaws in it.
-.\"
-.\" 2. The origin of this software must not be misrepresented, either by
-.\" explicit claim or by omission. Since few users ever read sources,
-.\" credits must appear in the documentation.
-.\"
-.\" 3. Altered versions must be plainly marked as such, and must not be
-.\" misrepresented as being the original software. Since few users
-.\" ever read sources, credits must appear in the documentation.
-.\"
-.\" 4. This notice may not be removed or altered.
-.\" %%%LICENSE_END
-.\"
-.\" In order to comply with `credits must appear in the documentation'
-.\" I added an AUTHOR paragraph below - aeb.
-.\"
-.\" In the default nroff environment there is no dagger \(dg.
-.\"
-.\" 2005-05-11 Removed discussion of `[[:<:]]' and `[[:>:]]', which
-.\" appear not to be in the glibc implementation of regcomp
-.\"
-.ie t .ds dg \(dg
-.el .ds dg (!)
-.TH REGEX 7 2009-01-12 "" "Linux Programmer's Manual"
-.SH NAME
-regex \- POSIX.2 regular expressions
-.SH DESCRIPTION
-Regular expressions ("RE"s),
-as defined in POSIX.2, come in two forms:
-modern REs (roughly those of
-.IR egrep ;
-POSIX.2 calls these "extended" REs)
-and obsolete REs (roughly those of
-.BR ed (1);
-POSIX.2 "basic" REs).
-Obsolete REs mostly exist for backward compatibility in some old programs;
-they will be discussed at the end.
-POSIX.2 leaves some aspects of RE syntax and semantics open;
-"\*(dg" marks decisions on these aspects that
-may not be fully portable to other POSIX.2 implementations.
-.PP
-A (modern) RE is one\*(dg or more nonempty\*(dg \fIbranches\fR,
-separated by \(aq|\(aq.
-It matches anything that matches one of the branches.
-.PP
-A branch is one\*(dg or more \fIpieces\fR, concatenated.
-It matches a match for the first, followed by a match for the second,
-and so on.
-.PP
-A piece is an \fIatom\fR possibly followed
-by a single\*(dg \(aq*\(aq, \(aq+\(aq, \(aq?\(aq, or \fIbound\fR.
-An atom followed by \(aq*\(aq
-matches a sequence of 0 or more matches of the atom.
-An atom followed by \(aq+\(aq
-matches a sequence of 1 or more matches of the atom.
-An atom followed by \(aq?\(aq
-matches a sequence of 0 or 1 matches of the atom.
-.PP
-A \fIbound\fR is \(aq{\(aq followed by an unsigned decimal integer,
-possibly followed by \(aq,\(aq
-possibly followed by another unsigned decimal integer,
-always followed by \(aq}\(aq.
-The integers must lie between 0 and
-.B RE_DUP_MAX
-(255\*(dg) inclusive,
-and if there are two of them, the first may not exceed the second.
-An atom followed by a bound containing one integer \fIi\fR
-and no comma matches
-a sequence of exactly \fIi\fR matches of the atom.
-An atom followed by a bound
-containing one integer \fIi\fR and a comma matches
-a sequence of \fIi\fR or more matches of the atom.
-An atom followed by a bound
-containing two integers \fIi\fR and \fIj\fR matches
-a sequence of \fIi\fR through \fIj\fR (inclusive) matches of the atom.
-.PP
-An atom is a regular expression enclosed in "\fI()\fP"
-(matching a match for the regular expression),
-an empty set of "\fI()\fP" (matching the null string)\*(dg,
-a \fIbracket expression\fR (see below), \(aq.\(aq
-(matching any single character), \(aq^\(aq (matching the null string at the
-beginning of a line), \(aq$\(aq (matching the null string at the
-end of a line), a \(aq\e\(aq followed by one of the characters
-"\fI^.[$()|*+?{\e\fP"
-(matching that character taken as an ordinary character),
-a \(aq\e\(aq followed by any other character\*(dg
-(matching that character taken as an ordinary character,
-as if the \(aq\e\(aq had not been present\*(dg),
-or a single character with no other significance (matching that character).
-A \(aq{\(aq followed by a character other than a digit is an ordinary
-character, not the beginning of a bound\*(dg.
-It is illegal to end an RE with \(aq\e\(aq.
-.PP
-A \fIbracket expression\fR is a list of characters enclosed in "\fI[]\fP".
-It normally matches any single character from the list (but see below).
-If the list begins with \(aq^\(aq,
-it matches any single character
-(but see below) \fInot\fR from the rest of the list.
-If two characters in the list are separated by \(aq\-\(aq, this is shorthand
-for the full \fIrange\fR of characters between those two (inclusive) in the
-collating sequence,
-for example, "\fI[0\-9]\fP" in ASCII matches any decimal digit.
-It is illegal\*(dg for two ranges to share an
-endpoint, for example, "\fIa-c-e\fP".
-Ranges are very collating-sequence-dependent,
-and portable programs should avoid relying on them.
-.PP
-To include a literal \(aq]\(aq in the list, make it the first character
-(following a possible \(aq^\(aq).
-To include a literal \(aq\-\(aq, make it the first or last character,
-or the second endpoint of a range.
-To use a literal \(aq\-\(aq as the first endpoint of a range,
-enclose it in "\fI[.\fP" and "\fI.]\fP"
-to make it a collating element (see below).
-With the exception of these and some combinations using \(aq[\(aq (see next
-paragraphs), all other special characters, including \(aq\e\(aq, lose their
-special significance within a bracket expression.
-.PP
-Within a bracket expression, a collating element (a character,
-a multicharacter sequence that collates as if it were a single character,
-or a collating-sequence name for either)
-enclosed in "\fI[.\fP" and "\fI.]\fP" 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 containing a multicharacter collating element
-can thus match more than one character,
-for example, if the collating sequence includes a "ch" collating element,
-then the RE "\fI[[.ch.]]*c\fP" matches the first five characters
-of "chchcc".
-.PP
-Within a bracket expression, a collating element enclosed in "\fI[=\fP" and
-"\fI=]\fP" 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 "\fI[.\fP" and "\fI.]\fP".)
-For example, if o and \o'o^' are the members of an equivalence class,
-then "\fI[[=o=]]\fP", "\fI[[=\o'o^'=]]\fP",
-and "\fI[o\o'o^']\fP" are all synonymous.
-An equivalence class may not\*(dg be an endpoint
-of a range.
-.PP
-Within a bracket expression, the name of a \fIcharacter class\fR enclosed
-in "\fI[:\fP" and "\fI:]\fP" stands for the list
-of all characters belonging to that
-class.
-Standard character class names are:
-.PP
-.RS
-.TS
-l l l.
-alnum digit punct
-alpha graph space
-blank lower upper
-cntrl print xdigit
-.TE
-.RE
-.PP
-These stand for the character classes defined in
-.BR wctype (3).
-A locale may provide others.
-A character class may not be used as an endpoint of a range.
-.\" As per http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=295666
-.\" The following does not seem to apply in the glibc implementation
-.\" .PP
-.\" There are two special cases\*(dg of bracket expressions:
-.\" the bracket expressions "\fI[[:<:]]\fP" and "\fI[[:>:]]\fP" match
-.\" the null string at the beginning and end of a word respectively.
-.\" A word is defined as a sequence of
-.\" word characters
-.\" which is neither preceded nor followed by
-.\" word characters.
-.\" A word character is an
-.\" .I alnum
-.\" character (as defined by
-.\" .BR wctype (3))
-.\" or an underscore.
-.\" This is an extension,
-.\" compatible with but not specified by POSIX.2,
-.\" and should be used with
-.\" caution in software intended to be portable to other systems.
-.PP
-In the event that an RE could match more than one substring of a given
-string,
-the RE matches the one starting earliest in the string.
-If the RE could match more than one substring starting at that point,
-it matches the longest.
-Subexpressions also match the longest possible substrings, subject to
-the constraint that the whole match be as long as possible,
-with subexpressions starting earlier in the RE taking priority over
-ones starting later.
-Note that higher-level subexpressions thus take priority over
-their lower-level component subexpressions.
-.PP
-Match lengths are measured in characters, not collating elements.
-A null string is considered longer than no match at all.
-For example,
-"\fIbb*\fP" matches the three middle characters of "abbbc",
-"\fI(wee|week)(knights|nights)\fP"
-matches all ten characters of "weeknights",
-when "\fI(.*).*\fP" is matched against "abc" the parenthesized subexpression
-matches all three characters, and
-when "\fI(a*)*\fP" is matched against "bc"
-both the whole RE and the parenthesized
-subexpression match the null string.
-.PP
-If case-independent matching is specified,
-the effect is much as if all case distinctions had vanished from the
-alphabet.
-When an alphabetic that exists in multiple cases appears as an
-ordinary character outside a bracket expression, it is effectively
-transformed into a bracket expression containing both cases,
-for example, \(aqx\(aq becomes "\fI[xX]\fP".
-When it appears inside a bracket expression, all case counterparts
-of it are added to the bracket expression, so that, for example, "\fI[x]\fP"
-becomes "\fI[xX]\fP" and "\fI[^x]\fP" becomes "\fI[^xX]\fP".
-.PP
-No particular limit is imposed on the length of REs\*(dg.
-Programs intended to be portable should not employ REs longer
-than 256 bytes,
-as an implementation can refuse to accept such REs and remain
-POSIX-compliant.
-.PP
-Obsolete ("basic") regular expressions differ in several respects.
-\(aq|\(aq, \(aq+\(aq, and \(aq?\(aq are
-ordinary characters and there is no equivalent
-for their functionality.
-The delimiters for bounds are "\fI\e{\fP" and "\fI\e}\fP",
-with \(aq{\(aq and \(aq}\(aq by themselves ordinary characters.
-The parentheses for nested subexpressions are "\fI\e(\fP" and "\fI\e)\fP",
-with \(aq(\(aq and \(aq)\(aq by themselves ordinary characters.
-\(aq^\(aq is an ordinary character except at the beginning of the
-RE or\*(dg the beginning of a parenthesized subexpression,
-\(aq$\(aq is an ordinary character except at the end of the
-RE or\*(dg the end of a parenthesized subexpression,
-and \(aq*\(aq is an ordinary character if it appears at the beginning of the
-RE or the beginning of a parenthesized subexpression
-(after a possible leading \(aq^\(aq).
-.PP
-Finally, there is one new type of atom, a \fIback reference\fR:
-\(aq\e\(aq followed by a nonzero decimal digit \fId\fR
-matches the same sequence of characters
-matched by the \fId\fRth parenthesized subexpression
-(numbering subexpressions by the positions of their opening parentheses,
-left to right),
-so that, for example, "\fI\e([bc]\e)\e1\fP" matches "bb" or "cc" but not "bc".
-.SH BUGS
-Having two kinds of REs is a botch.
-.PP
-The current POSIX.2 spec says that \(aq)\(aq is an ordinary character in
-the absence of an unmatched \(aq(\(aq;
-this was an unintentional result of a wording error,
-and change is likely.
-Avoid relying on it.
-.PP
-Back references are a dreadful botch,
-posing major problems for efficient implementations.
-They are also somewhat vaguely defined
-(does
-"\fIa\e(\e(b\e)*\e2\e)*d\fP" match "abbbd"?).
-Avoid using them.
-.PP
-POSIX.2's specification of case-independent matching is vague.
-The "one case implies all cases" definition given above
-is current consensus among implementors as to the right interpretation.
-.\" As per http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=295666
-.\" The following does not seem to apply in the glibc implementation
-.\" .PP
-.\" The syntax for word boundaries is incredibly ugly.
-.SH AUTHOR
-.\" Sigh... The page license means we must have the author's name
-.\" in the formatted output.
-This page was taken from Henry Spencer's regex package.
-.SH SEE ALSO
-.BR grep (1),
-.BR regex (3)
-.PP
-POSIX.2, section 2.8 (Regular Expression Notation).
-.SH COLOPHON
-This page is part of release 3.79 of the Linux
-.I man-pages
-project.
-A description of the project,
-information about reporting bugs,
-and the latest version of this page,
-can be found at
-\%http://www.kernel.org/doc/man\-pages/.
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