Learning Perl 6

Chapter 15. Regular Expressions

Regular expressions (or regexes) are patterns that describe a possible set of matching texts. They are a little language of their own, and many characters have a special meaning inside patterns. They may look cryptic at first, but after you learn them you have quite a bit of power.

Forget what you’ve seen about patterns in other languages. The Perl 6 pattern syntax started over. It’s less compact but also more powerful. In some cases it acts a bit differently.

This chapter shows simple patterns that match particular characters or sets of characters. It’s just the start. In Chapter 16 you’ll see fancier patterns and the side effects of matching. In Chapter 17 you’ll take it all to the next level.

The Match Operator

A pattern describes a set of text values. The simple pattern abc describes all the values that have an a next to a b next to a c. The trick then is to decide if a particular value is in the set of matching values. There are no half or partial matches; it matches or it doesn’t.

A pattern inside m/.../ immediately applies itself to the value in $_. If the pattern is in the Str the match operator returns something that evaluates to True in a condition:

$_ = 'Hamadryas';
if m/Hama/ { put 'It matched!'; }
else       { put 'It missed!';  }

That’s a bit verbose. The conditional operator takes care of that:

put m/Hama/ ?? 'It matched!' !! 'It missed!';

You don’t have to match against $_. You can use the smart match to apply it to a different value. That’s the target: ...