negative regex for perl string substitution

Question

I'm trying to shorten all multiple spaces to one space, except for the first occurence of spaces (indentation).

I've found that this code will replace the first occurences:

$_ =~ s/^ +/ /;

So I thought, its negation will do what I want. But it does not:

$_ =~ s/!^ +/ /g;

What am I doing wrong?

Answer 1

You can change approach to the regex

s/\S\K +/ /g;

Answer 2

Exclamation mark is not negation in regex. At least, not like that.

What you need is negative lookbehind:

s/(?<!^)\s+/ /g;

Should do the trick.