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"). 

  —  C Development Set