PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

NAME

       regex.h — regular expression matching types

SYNOPSIS

       #include <regex.h>

DESCRIPTION

       The <regex.h> header shall define the structures and symbolic constants used by the regcomp(), regexec(),
       regerror(), and regfree() functions.

       The <regex.h> header shall define the regex_t structure type, which shall include at least the  following
       member:

           size_t    re_nsub    Number of parenthesized subexpressions.

       The <regex.h> header shall define the size_t type as described in <sys/types.h>.

       The  <regex.h>  header  shall define the regoff_t type as a signed integer type that can hold the largest
       value that can be stored in either a ptrdiff_t type or a ssize_t type.

       The <regex.h> header shall define the regmatch_t  structure  type,  which  shall  include  at  least  the
       following members:

           regoff_t    rm_so    Byte offset from start of string
                                to start of substring.
           regoff_t    rm_eo    Byte offset from start of string of the
                                first character after the end of substring.

       The  <regex.h>  header  shall  define  the  following  symbolic constants for the cflags parameter to the
       regcomp() function:

       REG_EXTENDED  Use Extended Regular Expressions.

       REG_ICASE     Ignore case in match.

       REG_NOSUB     Report only success or fail in regexec().

       REG_NEWLINE   Change the handling of <newline>.

       The <regex.h> header shall define the following symbolic  constants  for  the  eflags  parameter  to  the
       regexec() function:

       REG_NOTBOL    The  <circumflex>  character  ('^'),  when taken as a special character, does not match the
                     beginning of string.

       REG_NOTEOL    The <dollar-sign> ('$'), when taken as a special character,  does  not  match  the  end  of
                     string.

       The <regex.h> header shall define the following symbolic constants as error return values:

       REG_NOMATCH   regexec() failed to match.

       REG_BADPAT    Invalid regular expression.

       REG_ECOLLATE  Invalid collating element referenced.

       REG_ECTYPE    Invalid character class type referenced.

       REG_EESCAPE   Trailing <backslash> character in pattern.

       REG_ESUBREG   Number in \digit invalid or in error.

       REG_EBRACK    "[]" imbalance.

       REG_EPAREN    "\(\)" or "()" imbalance.

       REG_EBRACE    "\{\}" imbalance.

       REG_BADBR     Content  of  "\{\}"  invalid:  not a number, number too large, more than two numbers, first
                     larger than second.

       REG_ERANGE    Invalid endpoint in range expression.

       REG_ESPACE    Out of memory.

       REG_BADRPT    '?', '*', or '+' not preceded by valid regular expression.

       The following shall be declared as functions and may also be defined as macros. Function prototypes shall
       be provided.

           int    regcomp(regex_t *restrict, const char *restrict, int);
           size_t regerror(int, const regex_t *restrict, char *restrict, size_t);
           int    regexec(const regex_t *restrict, const char *restrict, size_t,
                      regmatch_t [restrict], int);
           void   regfree(regex_t *);

       The implementation may define additional macros or constants using names beginning with REG_.

       The following sections are informative.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       <sys_types.h>

       The System Interfaces volume of POSIX.1‐2017, regcomp()

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE  and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have  been  introduced
       during   the   conversion  of  the  source  files  to  man  page  format.  To  report  such  errors,  see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .