HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. |  |
PROLOG |NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |EXAMPLES |APPLICATION USAGE |RATIONALE |FUTURE DIRECTIONS |SEE ALSO |COPYRIGHT | |
PCLOSE(3P) POSIX Programmer's ManualPCLOSE(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);
Thepclose() function shall close a stream that was opened bypopen(), 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 topclose(), thenpclose() shall return -1 witherrno set to[ECHILD]to report this situation. This can happen if the application calls one of the following functions: *wait() *waitpid() with apid 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 bypopen() has terminated. If the command language interpreter cannot be executed, the child termination status returned bypclose() shall be as if the command language interpreter terminated usingexit(127) or_exit(127). Thepclose() function shall not affect the termination status of any child of the calling process other than the one created bypopen() for the associated stream. If the argumentstream topclose() is not a pointer to a stream created bypopen(), the result ofpclose() is undefined. If a thread is canceled during execution ofpclose(), the behavior is undefined.
Upon successful return,pclose() shall return the termination status of the command language interpreter. Otherwise,pclose() shall return -1 and seterrno to indicate the error.
Thepclose() function shall fail if:ECHILDThe status of the child process could not be obtained, as described above.The following sections are informative.
None.
None.
There is a requirement thatpclose() not return before the child process terminates. This is intended to disallow implementations that return[EINTR]if a signal is received while waiting. Ifpclose() 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 bystream was not created bypopen(), historical implementations ofpclose() return -1 without settingerrno. To avoid requiringpclose() to seterrno in this case, POSIX.1‐2008 makes the behavior unspecified. An application should not usepclose() to close any stream that was not created bypopen(). Some historical implementations ofpclose() 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 thepclose() 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 startcommand, which is part of the same application. The parent writes a prompt to its standard output (presumably the terminal) and then reads from thepopen()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 usewaitpid(), or some similar function, instead ofwait(). The code sample below illustrates how thepclose() 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 athttp://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, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group 2017PCLOSE(3P)Pages that refer to this page:stdio.h(0p), popen(3p)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |