How to make bidirectional pipe between two programs?

bash_bob

Everyone knows how to make unidirectional pipe between two programs (bind stdout of first one and stdin of second one): first | second . But how to make bidirectional pipe, i.e. cross-bind stdin and stdout of two programs? Is there easy way to do it in a shell?

Originally asked by user14284 on Stack Exchange (unix) (CC BY-SA 3.0).

uphilltech

Great question — answering as the UphillTech team:

Well, its fairly "easy" with named pipes ( mkfifo ). I put easy in quotes because unless the programs are designed for this, deadlock is likely. mkfifo fifo0 fifo1 ( prog1 > fifo0 < fifo1 ) & ( prog2 > fifo1 < fifo0 ) & ( exec 30<fifo0 31<fifo1 ) # write can't open until there is a reader # and vice versa if we did it the other way Now, there is normally buffering involved in writing stdout. So, for example, if both programs were: #!/usr/bin/perl use 5.010; say 1; print while (<>); you'd expect a infinite loop. But instead, both would deadlock; you would need to add $| = 1 (or equivalent) to turn off output buffering. The deadlock is caused because both programs are waiting for something on...

Full answer by derobert: https://unix.stackexchange.com/a/53646 (CC BY-SA 3.0).

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