I would like to echo the first paragraph of the above post.   And please don’t treat it as an “RTFM!” brush-off, because it is not.

perldoc pages are generally very well-written, and there are a great many of them which discuss regular expressions.   Some of them take a while to read, but it is time very well spent.   Regular expressions are one of the core power-tools of Perl, and these pages are the first and the best place to begin learning about them.