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

[Brent Yorgey]

Ooh, neat, I didn't even know about that option. =)

On Tue, Aug 28, 2012 at 08:40:09AM -0700, Matthew wrote:
> Not to further discourage you from experimenting, but xargs can also
> run commands in parallel. Check out the -P argument. :)
> 
> On Tue, Aug 28, 2012 at 8:19 AM, Hong Yang <hyangfji at gmail.com> wrote:
> > 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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> >> > http://www.haskell.org/mailman/listinfo/beginners
> >>
> >>
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