POPEN(3S) (C Programming Language Utilities) POPEN(3S)
NAME
popen, pclose - initiate pipe 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. Command consists of a shell
command line. Type is an I/O mode, either r for reading or
w for writing. The value returned is 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 as an output filter.
EXAMPLE
A typical call may be:
char *cmd = "ls *.c";
FILE *ptr;
if ((ptr = popen(cmd, "r")) != NULL)
while (fgets(buf, n, ptr) != NULL)
(void) printf("%s ",buf);
This will print in stdout [see stdio (3S)] all the file
Page 1 May 1989
POPEN(3S) (C Programming Language Utilities) POPEN(3S)
names in the current directory that have a ``.c'' suffix.
SEE ALSO
pipe(2), wait(2), fclose(3S), fopen(3S), stdio(3S),
system(3S).
DIAGNOSTICS
popen returns a NULL pointer if files or processes cannot be
created.
Pclose returns -1 if stream is not associated with a
``popened'' command.
WARNING
If the original and `` popened'' processes concurrently read
or write a common file, neither should use buffered I/O,
because the buffering gets all mixed up. Problems with an
output filter may be forestalled by careful buffer flushing,
e.g. with fflush [see fclose(3S)].
Page 2 May 1989