A pipe is an interprocess connection between file descriptors of two processes. A pipe is created with the POSIX pipe() function (from <unistd.h>). Shells create pipes between processes if the "|" symbol is used: "cmd1 | cmd2" directs the output of cmd1 to the input of cmd2. On Windows use CreatePipe(). This mechanism redirects standard input, standard output, and standard error into the calling process in .NET and Java.