Allow running bash shell commands

Current implementation of process library has limited usability. CreateProcess record stores CmdSpec field, which is either a RawCommand or ShellCommand. The problem is that:

• RawCommand command quotes and escapes the command parameters
• ShellCommand does no escaping but it runs command in sh shell

Corollary: there is no way to run bash command with unescaped parameters. As a result there is no way to run this command (and many others):

diff <(echo $ENV_FOO) <(echo $ENV_BAR)

Running it as a RawCommand (using proc function) fails because command line parameters are escaped and become incorrect. Running it as ShellCommand (using shell function) fails because this is not valid sh syntax. I propose to create function that allows user to run bash commands without escaping the parameters (or even better, run any shell the user wants). In other words this program:

import System.Exit
import System.Process

main :: IO ()
main = do
  (_, _, _, pid) <- createProcess (SOME_NEW_FUNCTION "diff" ["<(echo $FOO)", "<(echo $BAR)"] )
                                        { env = Just [("FOO","Foo"),("BAR","Bar")] }
  ecode <- waitForProcess pid
  case ecode of
    ExitSuccess   -> putStrLn "All’s right with the world!"
    ExitFailure _ -> putStrLn ":-("

should produce:

1c1
< Foo
---
> Bar

Trac metadata

Trac field	Value
Version	7.8.1-rc2
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/process
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