Question

Can any one help me to understand the difference between two approaches to regular expressions, with some suitable examples?

• greedy
• non-greedy

Thanks

Answer 1

Chekout http://www.regular-expressions.info/repeat.html.

Greediness refers to the quantity of times the regex engine will try to match certain set of characters. The way to state the “greediness” of a regex expression is using the special characters *, +, ? and {}.

Consider

str = "asdfasdfbbbb"
r1 = /b/
r2 = /(asdf)*/
r3 = /b{3}/
r4 = /.*/

Matching these regex against str will result in:

r1 matching “asdfasdf b bbb” (non-greedy, tries to match b just once)
r2 matching “asdfasdf bbbb” (greedy, tries to match asdf as many times as possible)
r3 matching “asdfasdf bbb b” (non-greedy, matches b exactly 3 times)
r4 matching “asdfasdfbbbb“ (ULTRA-greedy, matches almost any character as many times as possible)

As regex are means to represent specific text patterns, it’s not like greediness it’s a matter of approach. You will sometimes need to match three times foo(/(foo){3}/) or infinite times bar(/(bar)*/).