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

       regcomp, regexec, regerror, regfree - POSIX regex functions

       #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);

   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 may be 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

              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 argu-
              ments 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  immedi-
              ately  before  a  newline, regardless of whether eflags contains

   POSIX regex matching
       regexec() is used to match a null-terminated string against the precom-
       piled  pattern buffer, preg.  nmatch and pmatch are used to provide in-
       formation 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.

              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 di-
       mensioned to have at least nmatch elements.  These  are  filled  in  by
       regexec()  with  substring  match addresses.  The offsets of the subex-
       pression 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 el-
       ement 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 er-
       rbuf_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 failure.

       regexec() returns zero for a successful match or REG_NOMATCH for  fail-

       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 character.

              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  at-

       |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.

       grep(1), regex(7)

       The glibc manual section, Regular Expressions

       This  page  is  part of release 5.05 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                               2019-10-10                          REGEX(3)
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