Proposal: Add showCommandForUser to process:System.Process
conrad at metadecks.org
Sun Sep 12 19:44:59 EDT 2010
On 12 September 2010 21:24, Ian Lynagh <igloo at earth.li> wrote:
> 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.
I think this is an important use-case, and the need for cross-platform
support justifies having it in the library.
A related use-case which would also use this function is a --dry-run
option that just prints out the command without running it (like "make
-n", "darcs send --dry-run" etc.) which is useful for, um,
> 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
> be deprecated.
> The code already existed within System.Process; I've just rearranged it
> a bit:
> showCommandForUser :: FilePath -> [String] -> String
> showCommandForUser cmd args = unwords (map translate (cmd : args))
> translate :: String -> String
> #if mingw32_HOST_OS
> 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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