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@(#)pipe.2 8.1 (Berkeley) 6/4/93
$FreeBSD$
.Dd January 30, 2006 .Dt PIPE 2 .Os .Sh NAME .Nm pipe .Nd create descriptor pair for interprocess communication .Sh LIBRARY .Lb libc .Sh SYNOPSIS n unistd.h .Ft int .Fn pipe "int fildes[2]" .Sh DESCRIPTION The .Fn pipe system call creates a .Em pipe , which is an object allowing bidirectional data flow, and allocates a pair of file descriptors.
p By convention, the first descriptor is normally used as the .Em read end of the pipe, and the second is normally the .Em 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.
p A pipe that has had an end closed is considered .Em widowed . Writing on such a pipe causes the writing process to receive a .Dv 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.
p 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. .Sh RETURN VALUES .Rv -std pipe .Sh ERRORS The .Fn pipe system call will fail if: l -tag -width Er t Bq Er EMFILE Too many descriptors are active. t Bq Er ENFILE The system file table is full. t Bq Er ENOMEM Not enough kernel memory to establish a pipe. .El .Sh SEE ALSO .Xr sh 1 , .Xr fork 2 , .Xr read 2 , .Xr socketpair 2 , .Xr write 2 .Sh HISTORY The .Fn pipe function appeared in .At v3 .
p Bidirectional pipes were first used on .At V.4 .