REGEX(3)                    Linux Programmer's Manual                   REGEX(3)

       regcomp, regexec, regerror, regfree - POSIX regex functions

       #include <regex.h>

       int regcomp(regex_t *restrict preg, const char *restrict regex,
                   int cflags);
       int regexec(const regex_t *restrict preg, const char *restrict string,
                   size_t nmatch, regmatch_t pmatch[restrict], int eflags);

       size_t regerror(int errcode, const regex_t *restrict preg,
                   char *restrict errbuf, size_t errbuf_size);
       void regfree(regex_t *preg);

   POSIX regex compiling
       regcomp() is used to compile a regular expression into a form that is
       suitable for subsequent 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 compilation.

       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 buffer.

       cflags is the bitwise-or of zero or more of the following:

              Use POSIX Extended Regular Expression syntax when interpreting
              regex.  If not set, POSIX Basic Regular Expression syntax is used.

              Do not differentiate case.  Subsequent regexec() searches using
              this pattern buffer will be case insensitive.

              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.

              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 newline, regardless of whether eflags
              contains REG_NOTEOL.

   POSIX regex matching
       regexec() is used to match a null-terminated string against the
       precompiled pattern buffer, preg.  nmatch and pmatch are used to provide
       information regarding the location of any matches.  eflags is the
       bitwise-or of zero or more of the following flags:

              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.

              The match-end-of-line operator always fails to match (but see the
              compilation flag REG_NEWLINE above).

              Use pmatch[0] on the input string, starting at byte
              pmatch[0].rm_so and ending before byte pmatch[0].rm_eo.  This
              allows matching embedded NUL bytes and avoids a strlen(3) on large
              strings.  It does not use nmatch on input, and does not change
              REG_NOTBOL or REG_NEWLINE processing.  This flag is a BSD
              extension, not present in POSIX.

   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 structure elements will contain
       the value -1.

       The regmatch_t structure which is the type of pmatch is defined in

           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() returns zero for a successful compilation or an error code for

       regexec() returns zero for a successful match or REG_NOMATCH for failure.

       The following errors can be returned by regcomp():

              Invalid use of back reference operator.

              Invalid use of pattern operators such as group or list.

              Invalid use of repetition operators such as using '*' as the first

              Un-matched brace interval operators.

              Un-matched bracket list operators.

              Invalid collating element.

              Unknown character class name.

              Nonspecific error.  This is not defined by POSIX.2.

              Trailing backslash.

              Un-matched parenthesis group operators.

              Invalid use of the range operator; for example, the ending point
              of the range occurs prior to the starting point.

              Compiled regular expression requires a pattern buffer larger than
              64 kB.  This is not defined by POSIX.2.

              The regex routines ran out of memory.

              Invalid back reference to a subexpression.

       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        │

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

       #include <stdint.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <regex.h>

       #define ARRAY_SIZE(arr) (sizeof((arr)) / sizeof((arr)[0]))

       static const char *const str =
               "1) John Driverhacker;\n2) John Doe;\n3) John Foo;\n";
       static const char *const re = "John.*o";

       int main(void)
           static const char *s = str;
           regex_t     regex;
           regmatch_t  pmatch[1];
           regoff_t    off, len;

           if (regcomp(&regex, re, REG_NEWLINE))

           printf("String = \"%s\"\n", str);

           for (int i = 0; ; i++) {
               if (regexec(&regex, s, ARRAY_SIZE(pmatch), pmatch, 0))

               off = pmatch[0].rm_so + (s - str);
               len = pmatch[0].rm_eo - pmatch[0].rm_so;
               printf("#%d:\n", i);
               printf("offset = %jd; length = %jd\n", (intmax_t) off,
                       (intmax_t) len);
               printf("substring = \"%.*s\"\n", len, s + pmatch[0].rm_so);

               s += pmatch[0].rm_eo;


       grep(1), regex(7)

       The glibc manual section, Regular Expressions

       This page is part of release 5.11 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

GNU                                2021-03-22                           REGEX(3)