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PCLOSE(3P)                 POSIX Programmer's Manual                PCLOSE(3P)

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
       pclose - close a pipe stream to or from a process
SYNOPSIS
       #include <stdio.h>
       int pclose(FILE *stream);

DESCRIPTION
       The pclose() function shall close a stream that was opened by  popen(),
       wait for the command to terminate, and return the termination status of
       the process that was running the command  language  interpreter.   How-
       ever,  if  a  call  caused  the termination status to be unavailable to
       pclose(), then pclose() shall return -1 with errno set to  [ECHILD]  to
       report  this situation. This can happen if the application calls one of
       the following functions:
        * wait()
        * waitpid() with a pid argument less than or equal to 0  or  equal  to
          the process ID of the command line interpreter
        * Any    other    function    not    defined   in   this   volume   of
          IEEE Std 1003.1-2001 that could do one of the above
       In any case, pclose() shall not return before the child process created
       by popen() has terminated.
       If  the command language interpreter cannot be executed, the child ter-
       mination status returned by pclose() shall be as if  the  command  lan-
       guage interpreter terminated using exit(127) or _exit(127).
       The  pclose()  function  shall not affect the termination status of any
       child of the calling process other than the one created by popen()  for
       the associated stream.
       If the argument stream to pclose() is not a pointer to a stream created
       by popen(), the result of pclose() is undefined.
RETURN VALUE
       Upon successful return, pclose() shall return the termination status of
       the  command  language interpreter. Otherwise, pclose() shall return -1
       and set errno to indicate the error.
ERRORS
       The pclose() function shall fail if:
       ECHILD The status of the  child  process  could  not  be  obtained,  as
              described above.

       The following sections are informative.
EXAMPLES
       None.
APPLICATION USAGE
       None.
RATIONALE
       There  is  a  requirement  that  pclose()  not  return before the child
       process terminates. This is intended to disallow  implementations  that
       return  [EINTR]  if  a  signal  is  received while waiting. If pclose()
       returned before the child terminated, there would be  no  way  for  the
       application  to  discover  which  child  used to be associated with the
       stream, and it could not do the cleanup itself.
       If the stream pointed to by stream was not created by popen(), histori-
       cal  implementations  of  pclose() return -1 without setting errno.  To
       avoid   requiring   pclose()   to   set    errno    in    this    case,
       IEEE Std 1003.1-2001  makes  the  behavior unspecified.  An application
       should not use pclose() to close any stream that  was  not  created  by
       popen().
       Some  historical implementations of pclose() either block or ignore the
       signals SIGINT, SIGQUIT, and SIGHUP while waiting for the child process
       to  terminate.  Since  this  behavior is not described for the pclose()
       function in IEEE Std 1003.1-2001, such implementations are not conform-
       ing.  Also,  some historical implementations return [EINTR] if a signal
       is received, even though the child process has  not  terminated.   Such
       implementations are also considered non-conforming.
       Consider, for example, an application that uses:

              popen("command", "r")
       to  start  command,  which  is part of the same application. The parent
       writes a prompt to its standard output (presumably  the  terminal)  and
       then reads from the popen()ed stream. The child reads the response from
       the user, does some transformation on the response (pathname expansion,
       perhaps)  and  writes  the  result  to its standard output.  The parent
       process reads the result from the pipe, does  something  with  it,  and
       prints  another prompt. The cycle repeats. Assuming that both processes
       do appropriate buffer flushing, this would be expected to work.
       To conform to IEEE Std 1003.1-2001, pclose()  must  use  waitpid(),  or
       some similar function, instead of wait().
       The  code  sample  below illustrates how the pclose() function might be
       implemented on a system conforming to IEEE Std 1003.1-2001.

              int pclose(FILE *stream)
              {
                  int stat;
                  pid_t pid;

                  pid = <pid for process created for stream by popen()>
                  (void) fclose(stream);
                  while (waitpid(pid, &stat, 0) == -1) {
                      if (errno != EINTR){
                          stat = -1;
                          break;
                      }
                  }
                  return(stat);
              }
FUTURE DIRECTIONS
       None.
SEE ALSO
       fork(),  popen(),   waitpid(),   the   Base   Definitions   volume   of
       IEEE Std 1003.1-2001, <stdio.h>
COPYRIGHT
       Portions  of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003  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 .

IEEE/The Open Group                  2003                           PCLOSE(3P)