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Linux 2.6 - man page for pclose (linux section 3posix)

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

       pclose - close a pipe stream to or from a process

       #include <stdio.h>

       int pclose(FILE *stream);

       The  pclose()  function shall close a stream that was opened by popen(), wait for the com-
       mand 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 func-

	* 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

       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.

       Upon  successful  return, pclose() shall return the termination status of the command lan-
       guage interpreter. Otherwise, pclose() shall return -1  and  set  errno	to  indicate  the

       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.



       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 sys-
       tem 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;


       fork()  ,  popen()  ,  waitpid()  ,  the  Base Definitions volume of IEEE Std 1003.1-2001,

       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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					PCLOSE(P)

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