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

[Hong Yang]

Hi Brent,

Thanks for the xargs command info. I did not know it before.

The other reason I want to play with my mapm version is eventually I want
to make it concurrent.

Thanks again,

Hong

On Tue, Aug 28, 2012 at 10:08 AM, Brent Yorgey <byorgey at seas.upenn.edu>wrote:

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