POPEN(3)POPEN(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 ALSOpipe(2), fopen(3S), fclose(3S), system(3), wait(2), sh(1)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, for instance,
with fflush, see fclose(3S).
Popen always calls sh, never calls csh.
7th Edition May 15, 1985 POPEN(3)
