How to write a Ruby switch statement (case...when) with regex and backreferences?

Question

I know that I can write a Ruby case statement to check a match against a regular expressions. However, I'd like to use the match data in my return statement. Something like this semi-pseudocode:

foo = "10/10/2011"

case foo
    when /^([0-9][0-9])/
        print "the month is #{match[1]}"
    else
        print "something else"
end

How can I achieve that?

Thanks!

---

Just a note: I understand that I wouldn't ever use a switch statement for a simple case as above, but that is only one example. In reality, what I am trying to achieve is the matching of many potential regular expressions for a date that can be written in various ways, and then parsing it with Ruby's Date class accordingly.

Answer 1

The references to the latest regex matching groups are always stored in pseudo variables $1 to $9:

case foo
when /^([0-9][0-9])/
    print "the month is #{$1}"
else
    print "something else"
end

You can also use the $LAST_MATCH_INFO pseudo variable to get at the whole MatchData object. This can be useful when using named captures:

case foo
when /^(?<number>[0-9][0-9])/
    print "the month is #{$LAST_MATCH_INFO['number']}"
else
    print "something else"
end