Frequently Asked Questions

There is a several second delay before results appear when running runInteractiveCommand or similar with stdin. How do I eliminate this delay?

This can occur due to not terminating a process handle, or not closing a stdin handle after a call to a method such as runInteractiveCommand.

Consider:

(proc_in, proc_out, _, _) <- runInteractiveCommand "xargs ls -l"
hPutStr proc_in "/usr/local"
putStrLn =<< hGetContents proc_out

In this case, the solution is:

  (proc_in, proc_out, _, h) <- runInteractiveCommand "xargs ls -l"
  hPutStr proc_in "/usr/local"
  hFlush proc_in
  hClose proc_in
  output <- hGetContents proc_out
  waitForProcess h
  putStrLn output