Support for piping together two or more commands

[amigalemming]

I guess this has been asked for a thousand times, but I cannot find it in the Docs or FAQ.

I want to do this the proper way:

do (Stdout stream) <- cmd "producer"
   cmd_ "consumer" (StdinBS stream)

However, it will not work, because consumer is only started after producer finished. I would need to add fork:

do (Stdout stream) <- fork $ cmd "producer"
   cmd_ "consumer" (StdinBS stream)

But we are in the Action monad, thus no fork available. :-(

If a pipe connection is currently not possible, then please implement it. If it is already possible, please document it. At least, this ticket might be an anchor for other ones looking for a solution.

[simonmichael]

I think this is different what what you're wanting, but for others searching: this works:

  -- run a pipe with a single cmd invocation
  newitems <- fromStdout <$> (cmd Shell "set -o pipefail; foo | bar" :: Action (Stdout String))

The shell pipefail setting is needed, otherwise errors in foo would not stop the shake action.