POPEN(3S) — HP-UX

NAME

popen, pclose − initiate pipe I/O to/from a process

SYNOPSIS

#include <stdio.h>

FILE ∗popen (command, type)
char ∗command, ∗type;

int pclose (stream)
FILE ∗stream;

DESCRIPTION

Popen creates a pipe between the calling program and the command to be executed.

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 may 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 “popened” command.

WARNINGS

If the original and “popened” 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 may be forestalled by careful buffer flushing, e.g., with fflush; see fclose(3S).

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