How to flush a pipe using bash

Question

I have a script that writes to a named pipe and another that reads from the pipe. Occasionally, when starting the script I have noticed that the contents of the pipe exist from a previous run of the script. Is there a way to flush out the pipe at the beginning of the script?

Answer 1

You can read from the pipe until it is empty. This will effectively flush it.

Before you attempt this daring feat, call fcntl(mypipe, F_SETFL, O_NONBLOCK) (I don't know the shell-scripting equivalent) to make a read when the pipe is empty not hang your program.

Answer 2

I think dd is your friend:

dd if=myfifo iflag=nonblock of=/dev/null

strace shows

open("myfifo", O_RDONLY|O_NONBLOCK)

and indeed doesn't even block on an empty fifo.

Answer 3

Try this:

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

from:

http://stackoverflow.com/questions/179291/setting-up-pipelines-reading-from-named-pipes-without-blocking-in-bash