readProcessWithExitCode is like
readProcess but with
two differences:
- it returns the ExitCode of the process, and does not throw
any exception if the code is not ExitSuccess.
- it reads and returns the output from process' standard error
handle, rather than the process inheriting the standard error
handle.
On Unix systems, see
waitForProcess for the meaning of exit
codes when the process died as the result of a signal.