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PIPE(2)			   Linux Programmer's Manual		       PIPE(2)

NAME
       pipe, pipe2 - create pipe

SYNOPSIS
       #include	<unistd.h>

       int pipe(int pipefd[2]);

       #define _GNU_SOURCE	       /* See feature_test_macros(7) */
       #include	<fcntl.h>	       /* Obtain O_* constant definitions */
       #include	<unistd.h>

       int pipe2(int pipefd[2],	int flags);

DESCRIPTION
       pipe()  creates	a pipe,	a unidirectional data channel that can be used
       for interprocess	communication.	The array pipefd is used to return two
       file  descriptors  referring to the ends	of the pipe.  pipefd[0]	refers
       to the read end of the pipe.  pipefd[1] refers to the write end of  the
       pipe.   Data  written  to  the write end	of the pipe is buffered	by the
       kernel until it is read from the	read end of  the  pipe.	  For  further
       details,	see pipe(7).

       If  flags is 0, then pipe2() is the same	as pipe().  The	following val-
       ues can be bitwise ORed in flags	to obtain different behavior:

       O_NONBLOCK  Set the O_NONBLOCK file status flag on  the	two  new  open
		   file	 descriptions.	 Using	this flag saves	extra calls to
		   fcntl(2) to achieve the same	result.

       O_CLOEXEC   Set the close-on-exec (FD_CLOEXEC) flag on the two new file
		   descriptors.	  See  the  description	 of  the  same flag in
		   open(2) for reasons why this	may be useful.

RETURN VALUE
       On success, zero	is returned.  On error,	-1 is returned,	and  errno  is
       set appropriately.

ERRORS
       EFAULT pipefd is	not valid.

       EINVAL (pipe2())	Invalid	value in flags.

       EMFILE Too many file descriptors	are in use by the process.

       ENFILE The  system  limit  on  the  total number	of open	files has been
	      reached.

VERSIONS
       pipe2() was added to Linux in version 2.6.27; glibc support  is	avail-
       able starting with version 2.9.

CONFORMING TO
       pipe(): POSIX.1-2001.

       pipe2() is Linux-specific.

EXAMPLE
       The  following  program	creates	 a pipe, and then fork(2)s to create a
       child process; the child	inherits a duplicate set of  file  descriptors
       that  refer  to	the same pipe.	After the fork(2), each	process	closes
       the descriptors that it doesn't need for	the pipe (see  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.

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

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

	   if (argc != 2) {
	    fprintf(stderr, "Usage: %s <string>\n", argv[0]);
	    exit(EXIT_FAILURE);
	   }

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

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

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

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

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

	   } else {	       /* Parent writes	argv[1]	to pipe	*/
	       close(pipefd[0]);	  /* Close unused read end */
	       write(pipefd[1],	argv[1], strlen(argv[1]));
	       close(pipefd[1]);	  /* Reader will see EOF */
	       wait(NULL);		  /* Wait for child */
	       exit(EXIT_SUCCESS);
	   }
       }

SEE ALSO
       fork(2),	read(2), socketpair(2),	write(2), popen(3), pipe(7)

COLOPHON
       This  page  is  part of release 3.53 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found	at http://www.kernel.org/doc/man-pages/.

Linux				  2012-02-14			       PIPE(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | EXAMPLE | SEE ALSO | COLOPHON

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