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.

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. Problems 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").