HP-UX Reference (11i v2 04/09) - 3 Library Functions N-Z (vol 7)

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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

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

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

/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 fores-

talled by careful buffer ﬂushing, e.g., with fflush(); see fclose(3S).