pipe (2)

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(The comments found at the beginning of the groff file "man2/pipe.2freebsd".)

NAME

pipe pipe2 - create descriptor pair for interprocess communication

LIBRARY

Lb libc

SYNOPSIS

In unistd.h Ft int Fn pipe int fildes[2] Ft int Fn pipe2 int fildes[2] int flags

DESCRIPTION

The Fn pipe system call creates a pipe which is an object allowing bidirectional data flow, and allocates a pair of file descriptors.

The Fn pipe2 system call allows control over the attributes of the file descriptors via the Fa flags argument. Values for Fa flags are constructed by a bitwise-inclusive OR of flags from the following list, defined in In fcntl.h :

O_CLOEXEC

Set the close-on-exec flag for the new file descriptors.

O_NONBLOCK

Set the non-blocking flag for the ends of the pipe.

If the Fa flags argument is 0, the behavior is identical to a call to Fn pipe .

By convention, the first descriptor is normally used as the read end of the pipe, and the second is normally the write end so that data written to Fa fildes[1] appears on (i.e., can be read from) Fa 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 that has had an end 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 bidirectional nature of this implementation of pipes is not portable to older systems, so it is recommended to use the convention for using the endpoints in the traditional manner when using a pipe in one direction.

RETURN VALUES

Rv -std pipe

ERRORS

The Fn pipe and Fn pipe2 system calls will fail if:

Bq Er EMFILE

Too many descriptors are active.

Bq Er ENFILE

The system file table is full.

Bq Er ENOMEM

Not enough kernel memory to establish a pipe.

The Fn pipe2 system call will also fail if:

Bq Er EINVAL

The Fa flags argument is invalid.

SEE ALSO

sh(1), fork(2), read(2), socketpair(2), write(2)

HISTORY

The Fn pipe function appeared in AT&T System v3 .

Bidirectional pipes were first used on AT&T System V.4 .

The Fn pipe2 function appeared in Fx 10.0 .