jgoerzen:
So I have a need to write data to a POSIX named pipe (aka FIFO). Long story involving a command that doesn't have an option to read data from stdin, but can from a named pipe.
I have created the named pipe from Haskell no problem.
But I can't use writeFile to write data to it. Worse, it returns:
*** Exception: /tmp/bakroller.zD0xHj/fifo: openFile: does not exist (No such device or address)
which is completely false, as it *does* exist, and I can cat to it as expected. The call should block until everything is read on the remote end.
I thought maybe writeFile is being weird, so I tried:
openFile "/tmp/bakroller.zD0xHj/fifo" WriteMode
Hmm, I can get this to work, but only if I have another process waiting on the pipe already: $ mkfifo /tmp/pipe $ tail -f /tmp/pipe $ ghc -e 'writeFile "/tmp/pipe" "test"' testtesttesttest^C However, if I don't have 'tail' waiting on the pipe, it fails.
There is no logical reason I can see for this behavior. In fact, something must be going to *extra* effort to avoid writing to a named pipe, and I can't work out why. Named pipes are a standard, useful part of a system and shouldn't be ignored like this.
Interestingly, readFile works fine on a named pipe.
What's going on here? Am I going to have to resort to the System.Posix interface just to be able to write to a named pipe?
Something fishy. -- Don