popen(3S) STANDARD I/O FUNCTIONS popen(3S)
NAME
popen, pclose - initiate pipe to/from a process
SYNOPSIS
#include <stdio.h>
FILE *popen (const char *command, const char *type);
int pclose (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 [see
intro(3)]; 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
Here is an example of a typical call:
#include <stdio.h>
#include <stdlib.h>
main()
{
char *cmd = "/usr/bin/ls *.c";
char buf[BUFSIZ];
FILE *ptr;
if ((ptr = popen(cmd, "r")) != NULL)
while (fgets(buf, BUFSIZ, ptr) != NULL)
(void) printf("%s", buf);
return 0;
}
This program will print on the standard output [see
stdio(3S)] all the file names in the current directory that
have a .c suffix.
Last change: C Programming Language Utilities 1
popen(3S) STANDARD I/O FUNCTIONS popen(3S)
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.
NOTES
If the original and popened processes concurrently read or
write a common file, neither should use buffered I/O. Prob-
lems with an output filter may be forestalled by careful
buffer flushing, e.g., with fflush [see fclose(3S)].
A security hole exists through the IFS and PATH environment
variables. Full pathnames should be used (or PATH reset)
and IFS should be set to space and tab (" \t").
Last change: C Programming Language Utilities 2