[Haskell-beginners] "system" call uses a different shell, or does not pick up the whole environment

[Brent Yorgey]

I do not know the solution to your problem -- dealing with shells,
environments, etc. can be tricky.

However, do you know about the 'xargs' command?  E.g. your example
could be accomplished with

  ls | xargs -L 1 -I{} cp -pr {} destination_dir/{}

-Brent

On Tue, Aug 28, 2012 at 09:58:16AM -0500, Hong Yang wrote:
> Hi,
> 
> I am trying to mimic mapM() at shell command line. I define the interface
> as "mapm cmd2 cmd1," so cmd2 will be run for each of the cmd1 results. "$_"
> can be used inside cmd2 to represent the current cmd1 result.
> 
> For example, the command
>         mapm    'cp -pr $_ destination_dir/$_'    ls
> copies everything under the current directory to the destination directory.
> 
> The code is as follows:
> 
> --
> module Main where
> 
> import System.Environment ( getArgs )
> import System.Exit
> import System.IO
> import System.Process
> import Text.Regex
> import Text.Regex.Posix
> 
> main = do
>     hs_argv <- getArgs
>     if length hs_argv /= 2
>       then
>         putStrLn "wrong arguments!" >> exitFailure
>       else do
>         let [cmd2, cmd1] = hs_argv
>         (_, hOut, hErr, _) <- runInteractiveCommand cmd1
>         err <- hGetContents hErr
>         hClose hErr
>         if null err
>           then do
>             out <- hGetContents hOut
>             mapM (f cmd2) (lines out)
>           else
>             putStr err >> exitFailure
> 
> f :: String -> String -> IO ExitCode
> f cmd2 item = system cmd2'
>   where cmd2' = if cmd2 =~ "\\$\\_"::Bool
>                 then subRegex (mkRegex "\\$\\_") cmd2 item
>                 else cmd2
> --
> 
> It works, except one issue that is bothering me.
> 
> If I issue
>         mapm    'lt $_'    ls,
> I get a bunch of
>         /bin/sh: lt: command not found,
> while I expect it act the same as
>         mapm    'ls -Alrt --color=auto $_'    ls,
> because "lt" is aliased to "ls -Alrt --color=auto."
> 
> Notice "/bin/sh" above. My shell is actually tcsh. All the aliases are in
> ~/.cshrc.
> 
> I tried replacing "system cmd2'" with
>         system ("source ~/.cshrc; " ++ cmd2')
>     and
>         system ("tcsh -c " ++ "'source ~/.cshrc; " ++ cmd2' ++ "'"),
> but they did not solve the problem.
> 
> Can someone please help me?
> 
> Thanks,
> 
> Hong

> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners