Proposal: Add showCommandForUser to process:System.Process
igloo at earth.li
Sun Sep 12 08:24:24 EDT 2010
Add showCommandForUser to process:System.Process
There are many programs (e.g. ghc and Cabal) which run other programs,
and when run with -v want to show the user what they are running. The
user then often wants to run the command by hand, in order to debug a
problem, but this can be tricky when the command or its arguments
include spaces or other characters treated specially by shells.
This proposal is for a System.Process.showCommandForUser function in the
process package, such that showCommandForUser cmd args can be copied and
pasted directly into a shell.
I would have put this in System.Cmd, except that module is earmarked to
The code already existed within System.Process; I've just rearranged it
showCommandForUser :: FilePath -> [String] -> String
showCommandForUser cmd args = unwords (map translate (cmd : args))
translate :: String -> String
translate str = '"' : snd (foldr escape (True,"\"") str)
where escape '"' (b, str) = (True, '\\' : '"' : str)
escape '\\' (True, str) = (True, '\\' : '\\' : str)
escape '\\' (False, str) = (False, '\\' : str)
escape c (b, str) = (False, c : str)
translate str = '\'' : foldr escape "'" str
where escape '\'' = showString "'\\''"
escape c = showChar c
The fallback for rawSystem is now
rawSystem cmd args = system (showCommandForUser cmd args)
except with hugs on Windows, where for some reason it's
rawSystem cmd args = system (cmd ++ showCommandForUser "" args)
which is surely wrong, but how it behaved before.
Discussion period: 2 weeks, until 26 Sep 2010.
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