pclose(3p) — Linux manual page


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.1‐2017
           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

       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         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




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

       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;



SEE ALSO         top

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

       The Base Definitions volume of POSIX.1‐2017, stdio.h(0p)

COPYRIGHT         top

       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(3P)

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