Well, let's go through this a step at a time. You want to search for 2 or more consecutive spaces. There are two ways to do that: /  +/ and / {2,}/. I normally use the first one, as that's what I think looks best.

Second, you want to make a substitution. Enter $var =~ s/.../.../;. Now we have this: $foo =~ s/(  +)//;. We just need to come up with something to substitute in there.

Well, you want   for each space, so we want it repeated for the length of the spaces: " " x length $1.

Now to add that to our regular expression. The trick is to use the /e and /g modifiers, which interpret the second half of the substitution as an expression and substitute globally. $foo =~ s/(  +)/" " x length $1/ge And that's it! You're done!

Hope this helps,