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     pipe — create descriptor pair for interprocess communication


     Standard C Library (libc, -lc)


     #include <unistd.h>

     pipe(int fildes[2]);


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

     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 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 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

     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


     The pipe() function returns the value 0 if successful; otherwise the
     value -1 is returned and the global variable errno is set to indicate the


     The pipe() system call will fail if:

     [EMFILE]           Too many descriptors are active.

     [ENFILE]           The system file table is full.

     [ENOMEM]           Not enough kernel memory to establish a pipe.


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


     The pipe() function appeared in Version 3 AT&T UNIX.

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