regex(3)



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 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:

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

   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
       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  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
       <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 fail-
       ure.

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 64 kB.  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 Expressions

COLOPHON
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       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.

GNU                               2017-09-15                          REGEX(3)

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