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 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 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

       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,
       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 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 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(P)