optional regex match?

Question

How can I match an optional character in a regex expression?

I am trying to write a small file that does a little housekeeping to our NAS.

The script goes through the folders inside the specified root folder.

For my testing the root is C:\Users\Solignis\Desktop\Orders

This is where I have the first match take place, it checks to be sure the file matches our standard name convention which is the city + 3 digit folder + 3 digit file number.

Sometimes though we have extra files that have a _1 or _2 on them to denote an additional page.

How can I make this regex expression also fit the "optional" _1 or _2 and sometimes _3 into the match?

The code:

$file =~ /^ ((C[A|F|L]|ME)) (\d{3}) (\d{3}) \. (PDF) /xmi

I am sure this is easy bit I still got loops on the brain from having to "drill" into this giant hash of arrays I made which is something like 25k files in some of the arrays.

Any help would be much appreciated.

Thanks

Answer 1

Something like (_[1-3])?

? Matches zero or one instance.

might be what you are looking for.

Answer 2

Something like (?: _[1-3] )? if don't want to catch this group.