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@(#)pipe.2 8.1 (Berkeley) 6/4/93
$FreeBSD: releng/11.0/lib/libc/sys/pipe.2 303717 2016-08-03 16:10:53Z brooks $
.Dd July 20, 2016 .Dt PIPE 2 .Os .Sh NAME .Nm pipe , .Nm pipe2 .Nd create descriptor pair for interprocess communication .Sh LIBRARY .Lb libc .Sh SYNOPSIS n unistd.h .Ft int .Fn pipe "int fildes[2]" .Ft int .Fn pipe2 "int fildes[2]" "int flags" .Sh DESCRIPTION The .Fn pipe function creates a .Em pipe , which is an object allowing bidirectional data flow, and allocates a pair of file descriptors.
p 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 n fcntl.h : l -tag -width ".Dv O_NONBLOCK" t Dv O_CLOEXEC Set the close-on-exec flag for the new file descriptors. t Dv O_NONBLOCK Set the non-blocking flag for the ends of the pipe. .El
p If the .Fa flags argument is 0, the behavior is identical to a call to .Fn pipe .
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 IMPLEMENTATION NOTES The .Fn pipe function calls the .Fn pipe2 system call. As a result, system call traces such as those captured by .Xr dtrace 1 or .Xr ktrace 1 will show calls to .Fn pipe2 . .Sh RETURN VALUES .Rv -std pipe .Sh ERRORS The .Fn pipe and .Fn pipe2 system calls will fail if: l -tag -width Er t Bq Er EFAULT .Ar fildes argument points to an invalid memory location. 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
p The .Fn pipe2 system call will also fail if: l -tag -width Er t Bq Er EINVAL The .Fa flags argument is invalid. .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 .
p The .Fn pipe2 function appeared in .Fx 10.0 .
p The .Fn pipe function became a wrapper around .Fn pipe2 in .Fx 11.0 .