garnix-io/cradle

cradle

Conveniently run child processes:

{-# LANGUAGE ScopedTypeVariables #-}
import Cradle

main :: IO ()
main = do
  StdoutTrimmed stdout <- run $ cmd "echo" & addArgs ["Hello, World!"]
  print stdout
  -- prints "Hello, World!"

  -- `run` is polymorphic on the return type. Just by adding it to the pattern
  -- match, you can get things like the exit code and stderr:
  (exitCode :: ExitCode, StderrRaw stderr) <- run $ cmd "ls" & addArgs ["does-not-exist"]
  print exitCode
  -- prints ExitFailure 2
  print stderr
  -- prints "ls: cannot access 'does-not-exist': No such file or directory\n"

It does not run the processes through a shell, but rather is meant as a high-level interface to fork & exec.

Alternatives

• process: process is substantially lower level than cradle. That is, it allows for more control, and more options, but at the cost of a more complicated interface. (cradle uses process under the hood.)
• typed-process: A safer version of process. Still lower-level than cradle.
• turtle: turtle is a more ambitious library, including a number of system-related functionality (such as changing directories, looking up environment variables, etc.), as well as providing convenient functions for running common executables such as date and rm. cradle by contrast only runs specified processes.
• shake's cmd. This was the basis for cradle, which indeed started it's life as a factoring-out of the cmd logic into a separate library. Since then, the API has been cleaned up and generalized. Notable changes are separating cmd from run so functions can be more easily applied to the command; not being variadic in the arguments for better type inference; and removing CmdArguments class altogether in favor of a composition of ProcessConfiguration -> ProcessConfiguration functions.