REGEX

Section: C Library Functions (3)
Updated: 4 March 1983
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NAME

regex, re_comp, re_exec, recmp, re_compile, re_match - regular expression handler

SYNOPSIS

char *re_comp(s)
char *s;

re_exec(s)
char *s;

recmp(pattern,target)
char *pattern, *target;

#include <regex.h>
struct regex {
        char    expbuf[ESIZE];
        char    *braslist[NBRA];
        char    *braelist[NBRA];
        char    circf;
        char    *start, *end; /* pointers to occurrence in 's' */
};

struct regex *re_compile(s,fold)
char *s;
int fold;

re_match(s,r)
char *s;
struct regex *r;

DESCRIPTION

Re_comp compiles a string into an internal form suitable for pattern matching. Re_exec checks the argument string against the last string passed to re_comp.

Re_comp returns 0 if the string s was compiled successfully; otherwise a string containing an error message is returned. If re_comp is passed 0 or a null string, it returns without changing the currently compiled regular expression.

Re_exec returns 1 if the string s matches the last compiled regular expression, 0 if the string s failed to match the last compiled regular expression, and -1 if the compiled regular expression was invalid (indicating an internal error).

Recmp is analogous to strcmp(3), but takes a regular expression pattern and returns 0 if it is matched in the target string, 1 if not, or -1 on error (bad regular expression).

The strings passed to both re_comp and re_exec may have trailing or embedded newline characters; they are terminated by nulls. The regular expressions recognized are described in the manual entry for ed(1), given the above difference.

Re_compile returns a pointer to a regex structure. This information is also kept in the static area used by re_comp(); If the fold variable is true, the compiled regular expression will match either upper or lower case. It may be deallocated with free(). Re_match is the same as re_exec with an explicit regex buffer. After calling Re_match, the pointers r->start and r->end point to the beginning and end of the matched expression in s.

DIAGNOSTICS

Re_exec returns -1 for an internal error.

Re_comp returns one of the following strings if an error occurs:

No previous regular expression,
Regular expression too long,
unmatched \(,
missing ],
too many \(\) pairs,
unmatched \).

Re_compile returns NULL for any of these errors.