Setting up pipelines reading from named pipes without blocking in bash

Question

I\'m looking to call a subprocess with a file descriptor opened to a given pipe such that the open() call does not hang waiting for the other side of the pipe to receive a c

Answer 1

Opening the FD read/write rather than read-only when setting up the pipeline prevents blocking.

To be a bit more specific:

$ mkfifo /tmp/foobar.pipe
$ some_program --command-fd=5 5<>/tmp/foobar.pipe

prevents the undesired blocking behavior, as 5<>/tmp/foobar.pipe opens in RW mode (as opposed to opening in read-only mode as with 5</tmp/foobar.pipe) although O_NONBLOCK is still set. Thanks to waldner on irc://irc.freenode.org/#bash for this pointer.

Answer 2

The only way I know getting this kind of result is a hack:

mkfifo /tmp/foobar.in
mkfifo /tmp/foobar.out
( cat </tmp/foobar.in ) >/tmp/foobar.out &
some_program --command-fd=5 5</tmp/foobar.out

perhaps this helps :-)