Question

I’m using getArgs in my Haskell program to parse arguments from the command line. However, I’ve noticed that I have problems when I call my program like this:

runhaskell Main *.hs .

As you can imagine, Main looks at *.hs files in the . directory.

But there’s a problem. The code below doesn’t behave as I’d expect.

import System

main :: IO ()
main = do
    args <- getArgs
    print args

I want to see

args = ["*.hs","."]

but instead I see

args = ["file1.hs","file2.hs","file3.hs","."]

My program needs to expand the glob expression itself because it does it in multiple directories. But how can I have getArgs return the raw list of arguments instead of trying to be magical and do the parsing itself?

Answer 1

This isn’t haskell, this is your shell.

Normally file globs (like *.hs) are interpreted by the shell before the command is passed to haskell.

To see this try running

 runhaskell Main '*.hs' .

The single quotes will prevent your shell from interpreting the glob, and pass the argument as-is to runhaskell.