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 appears on (i.e., can be read from) fildes. This allows the output of one program to be sent to another program: the sources standard output is set up to be the write end of the pipe, and the sinks 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.
.Rv -std pipe
The pipe system call will fail if: