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REGEXP(3)	       FreeBSD Library Functions Manual		     REGEXP(3)

NAME
     regcomp, regexec, regsub, regerror	-- regular expression handlers

LIBRARY
     Compatibility Library (libcompat, -lcompat)

SYNOPSIS
     #include <regexp.h>

     regexp *
     regcomp(const char	*exp);

     int
     regexec(const regexp *prog, const char *string);

     void
     regsub(const regexp *prog,	const char *source, char *dest);

DESCRIPTION
     This interface is made obsolete by	regex(3).

     The regcomp(), regexec(), regsub(), and regerror()	functions implement
     egrep(1)-style regular expressions	and supporting facilities.

     The regcomp() function compiles a regular expression into a structure of
     type regexp, and returns a	pointer	to it.	The space has been allocated
     using malloc(3) and may be	released by free.

     The regexec() function matches a NUL-terminated string against the	com-
     piled regular expression in prog.	It returns 1 for success and 0 for
     failure, and adjusts the contents of prog's startp	and endp (see below)
     accordingly.

     The members of a regexp structure include at least	the following (not
     necessarily in order):

	   char	*startp[NSUBEXP];
	   char	*endp[NSUBEXP];

     where NSUBEXP is defined (as 10) in the header file.  Once	a successful
     regexec() has been	done using the regexp(), each startp- endp pair
     describes one substring within the	string,	with the startp	pointing to
     the first character of the	substring and the endp pointing	to the first
     character following the substring.	 The 0th substring is the substring of
     string that matched the whole regular expression.	The others are those
     substrings	that matched parenthesized expressions within the regular
     expression, with parenthesized expressions	numbered in left-to-right
     order of their opening parentheses.

     The regsub() function copies source to dest, making substitutions accord-
     ing to the	most recent regexec() performed	using prog.  Each instance of
     `&' in source is replaced by the substring	indicated by startp[] and
     endp[].  Each instance of `\n', where n is	a digit, is replaced by	the
     substring indicated by startp[n] and endp[n].  To get a literal `&' or
     `\n' into dest, prefix it with `\'; to get	a literal `\' preceding	`&' or
     `\n', prefix it with another `\'.

     The regerror() function is	called whenever	an error is detected in
     regcomp(),	regexec(), or regsub().	 The default regerror()	writes the
     string msg, with a	suitable indicator of origin, on the standard error
     output and	invokes	exit(3).  The regerror() function can be replaced by
     the user if other actions are desirable.

REGULAR	EXPRESSION SYNTAX
     A regular expression is zero or more branches, separated by `|'.  It
     matches anything that matches one of the branches.

     A branch is zero or more pieces, concatenated.  It	matches	a match	for
     the first,	followed by a match for	the second, etc.

     A piece is	an atom	possibly followed by `*', `+', or `?'.	An atom	fol-
     lowed by `*' matches a sequence of	0 or more matches of the atom.	An
     atom followed by `+' matches a sequence of	1 or more matches of the atom.
     An	atom followed by `?' matches a match of	the atom, or the null string.

     An	atom is	a regular expression in	parentheses (matching a	match for the
     regular expression), a range (see below), `.'  (matching any single char-
     acter), `^' (matching the null string at the beginning of the input
     string), `$' (matching the	null string at the end of the input string), a
     `\' followed by a single character	(matching that character), or a	single
     character with no other significance (matching that character).

     A range is	a sequence of characters enclosed in `[]'.  It normally
     matches any single	character from the sequence.  If the sequence begins
     with `^', it matches any single character not from	the rest of the
     sequence.	If two characters in the sequence are separated	by `-',	this
     is	shorthand for the full list of ASCII characters	between	them (e.g.
     `[0-9]' matches any decimal digit).  To include a literal `]' in the
     sequence, make it the first character (following a	possible `^').	To
     include a literal `-', make it the	first or last character.

AMBIGUITY
     If	a regular expression could match two different parts of	the input
     string, it	will match the one which begins	earliest.  If both begin in
     the same place but	match different	lengths, or match the same length in
     different ways, life gets messier,	as follows.

     In	general, the possibilities in a	list of	branches are considered	in
     left-to-right order, the possibilities for	`*', `+', and `?' are consid-
     ered longest-first, nested	constructs are considered from the outermost
     in, and concatenated constructs are considered leftmost-first.  The match
     that will be chosen is the	one that uses the earliest possibility in the
     first choice that has to be made.	If there is more than one choice, the
     next will be made in the same manner (earliest possibility) subject to
     the decision on the first choice.	And so forth.

     For example, `(ab|a)b*c' could match `abc'	in one of two ways.  The first
     choice is between `ab' and	`a'; since `ab'	is earlier, and	does lead to a
     successful	overall	match, it is chosen.  Since the	`b' is already spoken
     for, the `b*' must	match its last possibility--the	empty string--since it
     must respect the earlier choice.

     In	the particular case where no `|'s are present and there	is only	one
     `*', `+', or `?', the net effect is that the longest possible match will
     be	chosen.	 So `ab*', presented with `xabbbby', will match	`abbbb'.  Note
     that if `ab*', is tried against `xabyabbbz', it will match	`ab' just
     after `x',	due to the begins-earliest rule.  (In effect, the decision on
     where to start the	match is the first choice to be	made, hence subsequent
     choices must respect it even if this leads	them to	less-preferred alter-
     natives.)

RETURN VALUES
     The regcomp() function returns NULL for a failure (regerror() permit-
     ting), where failures are syntax errors, exceeding	implementation limits,
     or	applying `+' or	`*' to a possibly-null operand.

SEE ALSO
     ed(1), egrep(1), ex(1), expr(1), fgrep(1),	grep(1), regex(3)

HISTORY
     Both code and manual page for regcomp(), regexec(), regsub(), and
     regerror()	were written at	the University of Toronto and appeared in
     4.3BSD-Tahoe.  They are intended to be compatible with the	Bell V8
     regexp(3),	but are	not derived from Bell code.

BUGS
     Empty branches and	empty regular expressions are not portable to V8.

     The restriction against applying `*' or `+' to a possibly-null operand is
     an	artifact of the	simplistic implementation.

     Does not support egrep's newline-separated	branches; neither does the V8
     regexp(3),	though.

     Due to emphasis on	compactness and	simplicity, it's not strikingly	fast.
     It	does give special attention to handling	simple cases quickly.

FreeBSD	11.0			 June 4, 1993			  FreeBSD 11.0

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | REGULAR EXPRESSION SYNTAX | AMBIGUITY | RETURN VALUES | SEE ALSO | HISTORY | BUGS

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