How does asterisk affect expressions in Ruby?

Question

I'm confused about why does asterisk have an impact on the regular expressions results in Ruby? Example codes are below:

2.3.0 :001 > "abbcccddddeeeee"[/z*/]
 => "" 
2.3.0 :002 > "abbcccddddeeeee"[/z/]
 => nil

Why the first one with * returns an empty string, while the other one returns nil?

Thanks!

score 1 · Answer 1 · answered Mar 07 '16 at 00:53

1

* is a quantifier that means "0 or more".

Your first snippet matches 0 instance of z. Your second snippet doesn't match anything.

answered Mar 07 '16 at 00:53

user229044

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score 0 · Answer 2 · answered Mar 07 '16 at 00:54

The Kleene star means "zero or more". In the first case, there are 0 zs in the string, which means that there is a match (actually even infinitely many matches) of "zero or more zs".

In the second case, you search for the occurrence of a single z in the string which doesn't exist.

How does asterisk affect expressions in Ruby?

2 Answers2