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, /bin/posix/sh (see sh-posix(1)).

The arguments to popen() are pointers to null-terminated strings containing, respectively, a shell command 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. 

RETURN VALUE

popen() returns a NULL pointer if files or processes cannot be created.  The success of the command execution 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 /bin/posix/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). 

STANDARDS CONFORMANCE

popen(): AES, SVID2, XPG2, XPG3, XPG4, POSIX.2

pclose(): AES, SVID2, XPG2, XPG3, XPG4, POSIX.2

Hewlett-Packard Company  —  HP-UX Release 9.0: August 1992