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);

MT-LEVEL

Unsafe

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. Because open files are shared, a type r command may be used as an input filter and a type w as an output filter. 

The environment of the executed command will be as if a child process were created within the popen() call using fork(2), and the child invoked the shell using the call:

Solaris execl("/usr/bin/sh", "sh", "-c", command, (char ∗)0);

XPG4 execl("/usr/bin/ksh", "ksh", "-c", command, (char ∗)0);

A stream opened by popen() should be closed by pclose(), which closes the pipe, and waits for the associated process to terminate and returns the termination status of the process running the command language interpreter.  This is the value returned by waitpid(2).  See wstat(5) for more details on termination status. 

RETURN VALUES

popen() returns a null pointer if files or processes cannot be created. 

pclose() returns the termination status of the command.  pclose() returns -1 if stream is not associated with a popen() command and sets errno to indicate the error. 

EXAMPLES

The following 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

ksh(1), pipe(2), wait(2), waitpid(2), fclose(3S), fopen(3S), stdio(3S), system(3S), wstat(5), xpg4(5)

NOTES

If the original and popen() 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, for example, 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"). 

SunOS 5.5.1  —  Last change: 17 Jul 1995