pipe

Also see named pipe (or FIFO).

In computer programming, especially in Unix operating systems, a pipe is a technique for passing information from one program process to another. Unlike other forms of interprocess communication (IPC), a pipe is one-way communication only. Basically, a pipe passes a parameter such as the output of one process to another process which accepts it as input. The system temporarily holds the piped information until it is read by the receiving process.

Using a UNIX shell (the UNIX interactive command interface), a pipe is specified in a command line as a simple vertical bar (|) between two command sequences. The output or result of the first command sequence is used as the input to the second command sequence. The pipe system call is used in a similar way within a program.

For two-way communication between processes, two pipes can be set up, one for each direction. A limitation of pipes for interprocess communication is that the processes using pipes must have a common parent process (that is, share a common open or initiation process and exist as the result of a fork system call from a parent process).

A pipe is fixed in size and is usually at least 4,096 bytes.

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