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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.  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 .