@(#)popen.3 6.2 (Berkeley) 12/07/88
POPEN 3 ""
.AT 3
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"
sh(1), pipe(2), wait4(2), fclose(3), fopen(3), system(3)
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, or if stream already `pclosed', or wait (4) returns an error.
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, for instance, with
fflush, see
fclose (3). Popen always calls sh , never calls csh .