Question

I am referring a regular expression cheat sheet.
It says

{3,5} means 3,4,and 5

{3,5}? means 3,4,5 ungreedy +

what does ungreedy +indicate?

Answer 1

The quanitifier {3,5}? means that it will try to match 3 occurrences first, then see if the rest of the expression matches. If the rest of the expression fails it will backtrack and try 4, then finally 5.

The greedy version {3,5} will try the matches in the opposite order – longest first.

Note that greediness does not affect whether or not a string matches. It only affects the order in which the engine performs the search, and the contents of the captures if there are capturing groups.

Here’s an example that demonstrates the difference. Imagine you have the string aaaaabc.

• (a{3,5})(\w*) will capture aaaaa and bc. (rubular)
• (a{3,5}?)(\w*) will capture aaa and aabc. (rubular)