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REGEX(3) - man page online | library functions

POSIX regex functions.

Chapter
2015-08-08
REGEX(3)                            Linux Programmer's Manual                            REGEX(3)

NAME

regcomp, regexec, regerror, regfree - POSIX regex functions

SYNOPSIS

#include <sys/types.h> #include <regex.h> int regcomp(regex_t *preg, const char *regex, int cflags); int regexec(const regex_t *preg, const char *string, size_t nmatch, regmatch_t pmatch[], int eflags); size_t regerror(int errcode, const regex_t *preg, char *errbuf, size_t errbuf_size); void regfree(regex_t *preg);

DESCRIPTION

POSIX regex compiling regcomp() is used to compile a regular expression into a form that is suitable for subse‐ quent regexec() searches. regcomp() is supplied with preg, a pointer to a pattern buffer storage area; regex, a pointer to the null-terminated string and cflags, flags used to determine the type of com‐ pilation. All regular expression searching must be done via a compiled pattern buffer, thus regexec() must always be supplied with the address of a regcomp() initialized pattern buf‐ fer. cflags may be the bitwise-or of zero or more of the following: REG_EXTENDED Use POSIX Extended Regular Expression syntax when interpreting regex. If not set, POSIX Basic Regular Expression syntax is used. REG_ICASE Do not differentiate case. Subsequent regexec() searches using this pattern buffer will be case insensitive. REG_NOSUB Do not report position of matches. The nmatch and pmatch arguments to regexec() are ignored if the pattern buffer supplied was compiled with this flag set. REG_NEWLINE Match-any-character operators don't match a newline. A nonmatching list ([^...]) not containing a newline does not match a newline. Match-beginning-of-line operator (^) matches the empty string immediately after a newline, regardless of whether eflags, the execution flags of regexec(), contains REG_NOTBOL. Match-end-of-line operator ($) matches the empty string immediately before a new‐ line, regardless of whether eflags contains REG_NOTEOL. POSIX regex matching regexec() is used to match a null-terminated string against the precompiled pattern buf‐ fer, preg. nmatch and pmatch are used to provide information regarding the location of any matches. eflags may be the bitwise-or of one or both of REG_NOTBOL and REG_NOTEOL which cause changes in matching behavior described below. REG_NOTBOL The match-beginning-of-line operator always fails to match (but see the compilation flag REG_NEWLINE above). This flag may be used when different portions of a string are passed to regexec() and the beginning of the string should not be interpreted as the beginning of the line. REG_NOTEOL The match-end-of-line operator always fails to match (but see the compilation flag REG_NEWLINE above). Byte offsets Unless REG_NOSUB was set for the compilation of the pattern buffer, it is possible to obtain match addressing information. pmatch must be dimensioned to have at least nmatch elements. These are filled in by regexec() with substring match addresses. The offsets of the subexpression starting at the ith open parenthesis are stored in pmatch[i]. The entire regular expression's match addresses are stored in pmatch[0]. (Note that to return the offsets of N subexpression matches, nmatch must be at least N+1.) Any unused struc‐ ture elements will contain the value -1. The regmatch_t structure which is the type of pmatch is defined in <regex.h>. typedef struct { regoff_t rm_so; regoff_t rm_eo; } regmatch_t; Each rm_so element that is not -1 indicates the start offset of the next largest substring match within the string. The relative rm_eo element indicates the end offset of the match, which is the offset of the first character after the matching text. POSIX error reporting regerror() is used to turn the error codes that can be returned by both regcomp() and regexec() into error message strings. regerror() is passed the error code, errcode, the pattern buffer, preg, a pointer to a character string buffer, errbuf, and the size of the string buffer, errbuf_size. It returns the size of the errbuf required to contain the null-terminated error message string. If both errbuf and errbuf_size are nonzero, errbuf is filled in with the first errbuf_size - 1 characters of the error message and a terminating null byte ('\0'). POSIX pattern buffer freeing Supplying regfree() with a precompiled pattern buffer, preg will free the memory allocated to the pattern buffer by the compiling process, regcomp().

RETURN VALUE

regcomp() returns zero for a successful compilation or an error code for failure. regexec() returns zero for a successful match or REG_NOMATCH for failure.

ERRORS

The following errors can be returned by regcomp(): REG_BADBR Invalid use of back reference operator. REG_BADPAT Invalid use of pattern operators such as group or list. REG_BADRPT Invalid use of repetition operators such as using '*' as the first character. REG_EBRACE Un-matched brace interval operators. REG_EBRACK Un-matched bracket list operators. REG_ECOLLATE Invalid collating element. REG_ECTYPE Unknown character class name. REG_EEND Nonspecific error. This is not defined by POSIX.2. REG_EESCAPE Trailing backslash. REG_EPAREN Un-matched parenthesis group operators. REG_ERANGE Invalid use of the range operator; for example, the ending point of the range occurs prior to the starting point. REG_ESIZE Compiled regular expression requires a pattern buffer larger than 64Kb. This is not defined by POSIX.2. REG_ESPACE The regex routines ran out of memory. REG_ESUBREG Invalid back reference to a subexpression.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7). ┌─────────────────────┬───────────────┬────────────────┐ │Interface │ Attribute │ Value │ ├─────────────────────┼───────────────┼────────────────┤ │regcomp(), regexec() │ Thread safety │ MT-Safe locale │ ├─────────────────────┼───────────────┼────────────────┤ │regerror() │ Thread safety │ MT-Safe env │ ├─────────────────────┼───────────────┼────────────────┤ │regfree() │ Thread safety │ MT-Safe │ └─────────────────────┴───────────────┴────────────────┘

CONFORMING TO

POSIX.1-2001, POSIX.1-2008.

SEE ALSO

grep(1), regex(7) The glibc manual section, Regular Expression Matching

COLOPHON

This page is part of release 4.04 of the Linux 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/.
GNU 2015-08-08 REGEX(3)
This manual Reference Other manuals
regex(3) referred by acpid(8) | argtable2(3) | ausearch_add_regex(3) | bash(1) | bash-static(1) | bmake(1) | cfingerd.conf(5) | dacs.conf(5) | dacs.exprs(5) | dacs_group(8) | dacs_transform(8) | dacscred(1) | dacstransform(1) | editrc(5) | editrc.tn(5) | filter-regex(8) | fortune(6) | killall(1) | nl_langinfo(3) | pattern(3bobcat)
refer to attributes(7) | grep(1) | regex(7)