exit status of command in a pipe line

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pipe

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 fur-
       ther details, see pipe(7).

       If flags is 0, then pipe2() is the same as pipe().  The following values 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 available 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>
", 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, "
", 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)

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