.\" Hey Emacs! This file is -*- nroff -*- source.
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.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
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.\" Modified by Michael Haardt <michael@moria.de>
.\" Modified 1993-07-23 by Rik Faith <faith@cs.unc.edu>
.\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 2004-06-17 by Michael Kerrisk <mtk-manpages@gmx.net>
.\"
.TH PIPE 2 2004-06-17 "Linux 2.6.7" "Linux Programmer's Manual"
.SH NAME
pipe \- create pipe
.SH SYNOPSIS
.B #include <unistd.h>
.sp
.BI "int pipe(int " filedes "[2]);"
.SH DESCRIPTION
.BR pipe ()
creates a pair of file descriptors, pointing to a pipe inode, and places
them in the array pointed to by
.IR filedes .
.I filedes[0]   
is for reading,
.I filedes[1]
is for writing.
.SH "RETURN VALUE"
On success, zero is returned.  On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EFAULT
.I filedes
is not valid.
.TP
.B EMFILE
Too many file descriptors are in use by the process.
.TP
.B ENFILE
The system limit on the total number of open files has been reached.
.SH "CONFORMING TO"
POSIX.1-2001.
.SH EXAMPLE
.\" fork.2 refers to this example program.
The following program creates a pipe, and then 
.BR fork (2)s 
to create a child process.  
After the 
.BR fork (2),
each process closes the descriptors that it doesn't need for the pipe
(see 
.BR pipe (7)).
The parent then writes the string contained in the program's 
command-line argument to the pipe, 
and the child reads this string a byte at a time from the pipe 
and echoes it on standard output.
.nf

#include <sys/wait.h>
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

int
main(int argc, char *argv[])
{
    int pfd[2];
    pid_t cpid;
    char buf;

    assert(argc == 2);

    if (pipe(pfd) == -1) { perror("pipe"); exit(EXIT_FAILURE); }

    cpid = fork();
    if (cpid == -1) { perror("fork"); exit(EXIT_FAILURE); }

    if (cpid == 0) {    /* Child reads from pipe */
        close(pfd[1]);          /* Close unused write end */

        while (read(pfd[0], &buf, 1) > 0)
            write(STDOUT_FILENO, &buf, 1);

        write(STDOUT_FILENO, "\\n", 1);
        close(pfd[0]);
        _exit(EXIT_SUCCESS);

    } else {            /* Parent writes argv[1] to pipe */
        close(pfd[0]);          /* Close unused read end */
        write(pfd[1], argv[1], strlen(argv[1]));
        close(pfd[1]);          /* Reader will see EOF */
        wait(NULL);             /* Wait for child */
        exit(EXIT_SUCCESS);
    }
}
.fi
.SH "SEE ALSO"
.BR fork (2),
.BR read (2),
.BR socketpair (2),
.BR write (2),
.BR popen (3),
.BR pipe (7)