How to use m! in Perl regex

Question

I'm learning Perl and about regular expressions for the first time so I apologize if this is a dumb question. I've been searching to find the answer for this myself but can't find anything. Maybe part of my problem is that I really don't know what it's called.

I came across a piece of code that looked like this:

$xl_file = "$curr_dir/$xl_file" unless $xl_file =~ ( m!(^[a-z]:)|[/\\]!i );

When I looked into the =~ operator I dove into the regex hole and started learning about that. But I only ever saw the "m//" matching operator. I'm assuming "m!" is another kind of matching operator but I can't find any references to it that explain how it works. Through experimentation i see that the "!i" is required when using it but that's about as much as I could figure out...

Could someone please explain this to me, or point me in the direction of some (free) material that can?

Answer 1

With matching operator, you can use any kind of delimiter, not just /.

So, all the below match operators are valid and do the same task:

m//
m!!
m{}
m##

Also note that, if you are using / as delimiter, you can remove that m from the beginning. So, /foo/ is valid, but !foo! is not.

Answer 2

No, it is the exact same thing. In Perl, you can choose regex delimiters as you like. That is,

m/foo/
/foo/
m!foo!
m"foo"
m+foo+
m xfoox
m{foo}

are all the same regex (but never use question marks as delimiter, they wake an ancient demon).

After the closing delimiter, regex modifiers are placed. The /i modifier activates case-insensitive matching.

For the full blast, you can dive into perlre for all the hidden nuggets of Perl regexes. But for the start, perlretut should be more appropriate.