pipe:
URL scheme#✎UNIX pipe access protocol.
Read and write from UNIX pipes.
The accepted syntax is:
pipe:[number]
number is the number corresponding to the file descriptor of the pipe (e.g. 0 for stdin, 1 for stdout, 2 for stderr). If number is not specified, by default the stdout file descriptor will be used for writing, stdin for reading.
[2] パイプ (コンピュータ) - Wikipedia () <https://ja.wikipedia.org/wiki/%E3%83%91%E3%82%A4%E3%83%97_(%E3%82%B3%E3%83%B3%E3%83%94%E3%83%A5%E3%83%BC%E3%82%BF)>
[5] AnyEvent::Util - search.cpan.org () <http://search.cpan.org/dist/AnyEvent/lib/AnyEvent/Util.pm#($r,_$w)_=_portable_pipe>