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PCLOSE(3P) POSIX Programmer's Manual PCLOSE(3P)
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.
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 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.
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.
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.
None.
None.
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);
}
None.
fork(3p), popen(3p), wait(3p)
The Base Definitions volume of POSIX.1‐2008, stdio.h(0p)
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)