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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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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.1‐2017
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.
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.1‐2017, stdio.h(0p)
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)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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