PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

       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         top

       pclose — close a pipe stream to or from a process

SYNOPSIS         top

       #include <stdio.h>

       int pclose(FILE *stream);

DESCRIPTION         top

       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.1‐2008
           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.

RETURN VALUE         top

       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         top

       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         top

       None.

APPLICATION USAGE         top

       None.

RATIONALE         top

       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         top

       None.

SEE ALSO         top

       fork(3p), popen(3p), wait(3p)

       The Base Definitions volume of POSIX.1‐2008, stdio.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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                 2013                          PCLOSE(3P)

Pages that refer to this page: stdio.h(0p)popen(3p)