Gabriel439 on Use Haskell for shell scripting

Comment on Use Haskell for shell scripting parent

How do you easily fork to run a command in the background?

`turtle` provides `fork` for running a command in the background. Example usage:

    example = do
        using (fork commandToForkInAnotherThread)
        theseCommandsStillRunInTheOriginalThread

> How does setting up pipes work?

See the `inproc` and `inshell` commands, which let you convert any shell command into a stream transformation embedded within Haskell.

What's the idiom for chdir'ing to a subdirectory such that you pop back out again when you're done (I'd use a subshell with (ch xxx; ...) in bash)?

You can write a combinator for this using `turtle` pretty easily:

    pushd newDir = do
        oldDir <- pwd
        cd newDir
        return (cd oldDir)

... and you use it like this:

    example = do
        popDir <- pushDir "/tmp"
        ... do stuff ...
        popDir

> what's the equivalent of <() in bash?

`inproc`/`inshell` which let you read in a command's standard output as a stream

barrkel 11y

FWIW:

<(foo) in bash creates a fifo, and pipes the output of foo to the fifo. It then replaces the whole <(foo) argument with the path to the fifo. This means that commands that normally expect to read from a file on the command line can instead be wired to read their input from a process. And, of course, both processes run concurrently.

(foo) does the same thing, except the other way around, for process output.

danidiaz 11y

There is a "createPipe" function in the "unix" package http://hackage.haskell.org/package/unix-2.7.1.0/docs/System-... that gets us half-way towards process substitution.

Unfortunately, I don't know how to get the name of the device file associated to the pipe, and I need it in order to pass it as an argument to the reading process :(

thinkpad20 11y

In my opinion it be nice to write it as a wrapper type thing:

    inDir d action = do
      oldDir <- pwd
      cd newDir
      result <- action
      cd oldDir
      return result

Then you could use it like a python `with` statement. :)

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