? makes a preceding quantifier lazy.
- This mark was also used for repetition, to say that something should happen either 0 or 1 time.
- In this use case, its context has a different meaning.
- Examples:
*?
- Something should be zero or one time.
+?
- Should use lazy behaviour to do the above.
{min,max}?
??- Instructs a quantifier to use a “lazy strategy” for making choices. Instead of the “greedy strategy”.
- Match as little as possible before giving control to the next expression part.
- Still defers to overall match.
- Not necessarily faster or slower.
/.*?[0-9]+/, which would match “Page 266”.
- The
? was added here, so the repetition should be lazy.
- Therefore the wildcard happens at the start of the string.
- Once it gets to
2, it says “can I give up yet”?
- That is this part of the expression:
.*?[0-9]
- However, it does not give up and switches to
+/, so therefore it goes through the numbers of “66”
- Thus all of the above matches “Page 266”.
- Another example is
/.*?[0-9]+?/ while trying to match “Page 266”
- It would only return “Page 2”
- Another example is
/\d+\w+\d+/ which finds “01_FY_07_report_99”
- This is a greedy example.
- Then with the
? with /\d+\w+?\d+/ would only match “01_FY_07” and nothing else.
- Tries to give up as quickly as it can, because it is lazy.
- A third example is:
/".+", ".+"/ would match “Milton”, “Waddams”, “Initech, Inc.” (including the commas as well)
- Whereas
/".+?", ".+?"/ would match “Milton”, “Waddams” and “Initech, Inc.”