HP-UX Reference (11i v1 00/12) - 3 Library Functions N-Z (vol 7)
__________________________________________________________________________________________________________________________________________________________________________________________________
__________________________________________________________________________________________________________________________________________________________________________________________________
STANDARD Printed by: Nora Chuang [nchuang] STANDARD
/build/1111/BRICK/man3/nan.3m
________________________________________________________________
___ ___
p
popen(3S) popen(3S)
NAME
popen(), pclose() - initiate pipe I/O to/from a process
SYNOPSIS
#include <stdio.h>
FILE *popen(const char *command, const char *type);
int pclose(FILE *stream);
DESCRIPTION
popen() creates a pipe between the calling program and a command to be executed by the POSIX shell,
/usr/bin/sh (see sh-posix(1)).
The arguments to popen() are pointers to null-terminated strings containing, respectively, a shell com-
mand line and an I/O mode, either r for reading or w for writing.
popen() returns a stream pointer such that one can write to the standard input of the command if the
I/O mode is w by writing to the file stream; and one can read from the standard output of the command if
the I/O mode is r by reading from the file stream.
A stream opened by
popen() should be closed by
pclose(), which waits for the associated process to
terminate and returns the exit status of the command.
Because open files are shared, a type
r command can be used as an input filter and a type
w command as
an output filter.
APPLICATION USAGE
popen() and pclose() are thread-safe. These interfaces are not async-cancel-safe. A cancellation
point may occur when a thread is executing popen() or pclose().
After a stream is associated with a pipe by popen(), the stream is byte-oriented (see orientation(5)).
RETURN VALUE
popen() returns a NULL pointer if files or processes cannot be created. The success of the command exe-
cution can be checked by examining the return value of pclose().
pclose() returns -1 if stream is not associated with a popen()ed command, or 127 if
/usr/bin/sh could not be executed for some reason.
WARNINGS
If the original and popen()ed processes concurrently read or write a common file, neither should use
buffered I/O because the buffering will not work properly. Problems with an output filter can be forestalled
by careful buffer flushing, e.g., with fflush(); see fclose(3S).
SEE ALSO
pipe(2), wait(2), fclose(3S), fopen(3S), system(3S), orientation(5).
STANDARDS CONFORMANCE
popen(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, POSIX.2
pclose(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, POSIX.2
Section 3−−616 − 1 − HP-UX Release 11i: December 2000
___
___