POPEN(3S) POPEN(3S)
NAME
popen, pclose - initiate I/O to/from a process
SYNOPSIS
#include <stdio.h>
FILE *popen(command, type)
char *command, *type;
pclose(stream)
FILE *stream;
DESCRIPTION
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. It
creates a pipe between the calling process and the command
to be executed. The value returned is a stream pointer that
can be used (as appropriate) to write to the standard input
of the command or read from its standard output.
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" as an output filter.
SEE ALSO
pipe(2), fopen(3), fclose(3), system(3), wait(2)
DIAGNOSTICS
Popen returns a null pointer if files or processes cannot be
created, or the Shell cannot be accessed.
Pclose returns -1 if stream is not associated with a
`popened' command.
BUGS
Buffered reading before opening an input filter may leave
the standard input of that filter mispositioned. Similar
problems with an output filter may be forestalled by careful
buffer flushing, e.g. with fflush, see fclose(3).