Learning Perl, 3rd Edition

Chapter 9. Using Regular Expressions

Now that we’ve seen what goes inside a regular expression, let’s take what we’ve learned back into Perl.

Matches with m//

We’ve been writing patterns in pairs of forward slashes, like /fred/. But this is actually a shortcut for the m// (pattern match) operator. As we saw with the qw// operator, you may choose any pair of delimiters to quote the contents. So, we could write that same expression as m(fred), m<fred>, m{fred}, or m[fred] using those paired delimiters, or as m,fred,, m!fred!, m^fred^, or many other ways using nonpaired delimiters.^[1]

The shortcut is that if you choose the forward slash as the delimiter, you may omit the initial m. Since Perl folks love to avoid typing extra characters, you’ll see most pattern matches written using slashes, as in /fred/.

Of course, you should wisely choose a delimiter that doesn’t appear in your pattern.^[2] If you wanted to make a pattern to match the beginning of an ordinary web URL, you might start to write /^http:\/\// to match the initial "http://". But that’s easier to read, write, maintain, and debug if you use a better choice of delimiter: m%^http://%.^[3]

It’s common to use curly braces as the delimiter. If you use a programmers’ text editor, it probably has the ability to jump from an opening curly brace to the corresponding closing one, which can be handy in maintaining code.

Option Modifiers

There are several option modifier letters, sometimes called flags , which may be appended as a ...