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



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

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.
       However, 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 POSIX.1-2017 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
       termination status returned by pclose() shall be as if the command
       language 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.

       If a thread is canceled during execution of pclose(), the behavior 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(),
       historical implementations of pclose() return -1 without setting errno.
       To avoid requiring pclose() to set errno in this case, POSIX.1-2008
       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 POSIX.1-2008, such implementations are not conforming.
       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 POSIX.1-2008, 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 POSIX.1-2008.


           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(), wait()

       The Base Definitions volume of POSIX.1-2017, <stdio.h>

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 .



IEEE/The Open Group                  2017                            PCLOSE(3)
