NAME

unistd - header file for symbolic constants

SYNOPSIS

#include <unistd.h>

DESCRIPTION

The <unistd.h> header file defines  the  symbolic  constants
and  structures which are not already defined or declared in
some other header. The contents of  this  header  are  shown
below.  The following symbolic constants are defined for the
access function [see access(2)]:
   R_OK   Test for read permission
   W_OK   Test for write permission
   X_OK   Test for execute (search) permission
   F_OK   Test for existence of file
The constants F_OK, R_OK, W_OK and X_OK and the  expressions
R_OK|W_OK,  R_OK|X_OK  and  R_OK|W_OK|X_OK all have distinct
values.  Declares the constant
   NULL   null pointer
The following symbolic constants are defined for  the  lockf
function [see lockf(3C)]:
   F_ULOCK   Unlock a previously locked region
   F_LOCK    Lock a region for exclusive use
   F_TLOCK   Test and lock a region for exclusive use
   F_TEST    Test a region for other processes locks
The following symbolic constants are defined for  the  lseek
[see lseek(2)] and fcntl [see fcntl(2)] functions (they have
distinct values):
   SEEK_SET   Set file offset to offset
   SEEK_CUR   Set file offset to current plus offset
   SEEK_END   Set file offset to EOF plus offset
The following symbolic constants  are  defined  (with  fixed
values):
   _POSIX_VERSION   Integer value indicating version
                    of the POSIX standard
   _XOPEN_VERSION   integer value indicating version of the XPG
                    to which system is compliant
The following symbolic constants  are  defined  to  indicate
that the option is present:
   _POSIX_JOB_CONTROL   implementation    sup-
                        ports job control
   _POSIX_SAVED_IDS     the   exec   functions
                        [see exec(2)] save the
                        effective   user   and
                        group

   _POSIX_VDISABLE      terminal special char-
                        acters    defined   in
                        <termios.h> [see  ter-
                        mio(7)]  can  be  dis-
                        abled using this char-
                        acter
The following symbolic constants  are  defined  for  sysconf
[see sysconf(3C)]:
   _SC_ARG_MAX
   _SC_CHILD_MAX
   _SC_CLK_TCK
   _SC_JOB_CONTROL
   _SC_NGROUPS_MAX
   _SC_OPEN_MAX
   _SC_PAGESIZE
   _SC_PASS_MAX
   _SC_SAVED_IDS
   _SC_VERSION
   _SC_XOPEN_VERSION
The following symbolic constants are  defined  for  pathconf
[see fpathconf(3C)]:
   _PC_CHOWN_RESTRICTED
   _PC_LINK_MAX
   _PC_MAX_CANON
   _PC_MAX_INPUT
   _PC_NAME_MAX
   _PC_NO_TRUNC
   _PC_PATH_MAX
   _PC_PIPE_BUF
   _PC_VDISABLE
The  following  symbolic  constants  are  defined  for  file
streams:
   STDIN_FILENO    File number of stdin.  It is 0.
   STDOUT_FILENO   File number of stout.  It is 1.
   STDERR_FILENO   File number of stderr.  It is 2.
The following pathnames are defined:
   GF_PATH   Pathname of the group file.
   PF_PATH   Pathname of the passwd file.

NOTES

The following values for  constants  are  defined  for  this
release of System V:
   _POSIX_VERSION   198808L
   _XOPEN_VERSION        3

SEE ALSO

access(2), exec(2), fcntl(2), lseek(2), termios(2),
fpathconf(3C), sysconf(3C), group(4), passwd(4), termio(7).