Why is my regular expression skipping the dot instead of matching the string before it?

Question

I was trying to work out a regular expression in IRB and got some unexpected output. The goal was to match everything up until the last dot in a FQDN.

So, for example, if I was trying to match the string "flowtechconsulting.com", I started with the following:

s1.sub(/^(.*)\\./, "\\1")   #=> "flowtechconsultingcom"

However, the sub function simply returned everything but the dot, instead of the first matching group.

If I add two matching groups it works:

s1.sub(/^(.*)\\.(.*)$/, "\\1")   #=> "flowtechconsulting"

I'm just not sure why the first doesn't work. It seems like it should.

Answer 1

/^(.*)\./ only captures everything up to the dot. The "com" is not captured and thus not replaced in the substitution.

Answer 2

Forget about sub, and do something like:

"foo.bar.baz.com"[/(.*)(?:\.)/, 1]
# => "foo.bar.baz"