pipe(2) [netbsd man page]
PIPE(2) BSD System Calls Manual PIPE(2) NAME
pipe -- create descriptor pair for interprocess communication LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <unistd.h> int pipe(int fildes[2]); int pipe2(int fildes[2], int flags); DESCRIPTION
The pipe() function creates a pipe, which is an object allowing unidirectional data flow, and allocates a pair of file descriptors. The first descriptor connects to the read end of the pipe, and the second connects to the write end, so that data written to fildes[1] appears on (i.e., can be read from) fildes[0]. This allows the output of one program to be sent to another program: the source's standard output is set up to be the write end of the pipe, and the sink's standard input is set up to be the read end of the pipe. The pipe itself persists until all its associated descriptors are closed. A pipe whose read or write end has been closed is considered widowed. Writing on such a pipe causes the writing process to receive a SIGPIPE signal. Widowing a pipe is the only way to deliver end-of-file to a reader: after the reader consumes any buffered data, reading a widowed pipe returns a zero count. The pipe2() function behaves exactly like pipe() only it allows extra flags to be set on the returned file descriptor. The following flags are valid: O_CLOEXEC Set the ``close-on-exec'' property. O_NONBLOCK Sets non-blocking I/O. O_NOSIGPIPE Return EPIPE instead of raising SIGPIPE. RETURN VALUES
On successful creation of the pipe, zero is returned. Otherwise, a value of -1 is returned and the variable errno set to indicate the error. ERRORS
The pipe() and pipe2() calls will fail if: [EFAULT] The fildes buffer is in an invalid area of the process's address space. The reliable detection of this error cannot be guaranteed; when not detected, a signal may be delivered to the process, indicating an address violation. [EMFILE] Too many descriptors are active. [ENFILE] The system file table is full. pipe2() will also fail if: [EINVAL] flags is other than O_NONBLOCK or O_CLOEXEC. SEE ALSO
sh(1), fork(2), read(2), socketpair(2), write(2) STANDARDS
The pipe() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1''). HISTORY
A pipe() function call appeared in Version 6 AT&T UNIX. The pipe2() function is inspired from Linux and appeared in NetBSD 6.0. BSD
January 23, 2012 BSD
Check Out this Related Man Page
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 #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 3.25 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 2009-09-15 PIPE(2)