man2/pipe.2

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   3 .\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
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  25 .\" Modified by Michael Haardt <michael@moria.de>
  26 .\" Modified 1993-07-23 by Rik Faith <faith@cs.unc.edu>
  27 .\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
  28 .\" Modified 2004-06-17 by Michael Kerrisk <mtk-manpages@gmx.net>
  29 .\"
  30 .TH PIPE 2 2004-06-17 "Linux 2.6.7" "Linux Programmer's Manual"
  31 .SH NAME
  32 pipe \- create pipe
  33 .SH SYNOPSIS
  34 .B #include <unistd.h>
  35 .sp
  36 .BI "int pipe(int " filedes "[2]);"
  37 .SH DESCRIPTION
  38 .BR pipe ()
  39 creates a pair of file descriptors, pointing to a pipe inode, and places
  40 them in the array pointed to by
  41 .IR filedes .
  42 .I filedes[0]
  43 is for reading,
  44 .I filedes[1]
  45 is for writing.
  46 .SH "RETURN VALUE"
  47 On success, zero is returned.  On error, \-1 is returned, and
  48 .I errno
  49 is set appropriately.
  50 .SH ERRORS
  51 .TP
  52 .B EFAULT
  53 .I filedes
  54 is not valid.
  55 .TP
  56 .B EMFILE
  57 Too many file descriptors are in use by the process.
  58 .TP
  59 .B ENFILE
  60 The system limit on the total number of open files has been reached.
  61 .SH "CONFORMING TO"
  62 POSIX.1
  63 .SH EXAMPLE
  64 .\" fork.2 refers to this example program.
  65 The following program creates a pipe, and then
  66 .BR fork (2)s
  67 to create a child process.
  68 After the
  69 .BR fork (2),
  70 each process closes the descriptors that it doesn't need for the pipe
  71 (see
  72 .BR pipe (7)).
  73 The parent then writes the string contained in the program's
  74 command-line argument to the pipe,
  75 and the child reads this string a byte at a time from the pipe
  76 and echoes it on standard output.
  77 .nf
  78
  79 #include <sys/wait.h>
  80 #include <assert.h>
  81 #include <stdio.h>
  82 #include <stdlib.h>
  83 #include <unistd.h>
  84 #include <string.h>
  85
  86 int
  87 main(int argc, char *argv[])
  88 {
  89     int pfd[2];
  90     pid_t cpid;
  91     char buf;
  92
  93     assert(argc == 2);
  94
  95     if (pipe(pfd) == -1) { perror("pipe"); exit(EXIT_FAILURE); }
  96
  97     cpid = fork();
  98     if (cpid == -1) { perror("fork"); exit(EXIT_FAILURE); }
  99
 100     if (cpid == 0) {    /* Child reads from pipe */
 101         close(pfd[1]);          /* Close unused write end */
 102
 103         while (read(pfd[0], &buf, 1) > 0)
 104             write(STDOUT_FILENO, &buf, 1);
 105
 106         write(STDOUT_FILENO, "\\n", 1);
 107         close(pfd[0]);
 108         _exit(EXIT_SUCCESS);
 109
 110     } else {            /* Parent writes argv[1] to pipe */
 111         close(pfd[0]);          /* Close unused read end */
 112         write(pfd[1], argv[1], strlen(argv[1]));
 113         close(pfd[1]);          /* Reader will see EOF */
 114         wait(NULL);             /* Wait for child */
 115         exit(EXIT_SUCCESS);
 116     }
 117 }
 118
 119 .fi
 120 .SH "SEE ALSO"
 121 .BR fork (2),
 122 .BR read (2),
 123 .BR socketpair (2),
 124 .BR write (2),
 125 .BR pipe (7)