- Regex engines are eager and greedy.
- An example of this is
/(peanut|peanutbutter) which only matches the “peanut” of “peanutbutter”
- This is because the regex engine reads from left to right.
- To rewrite this another way, we can use
/peanut(butter)?/ which then matches “peanutbutter” as a whole.
- We can also tell it to be lazy with
/peanut(butter)??/ which then matches only “peanut”
- Alternation regular expression for “abcdefghijklmnopqrstuvwxyz”
/(abc|def|ghi|jkl)/
- If you remove the global flag, it will only match “abc”
- Adding in
/(xyz|abc|def|ghi|jkl)/ will also only match “abc”
/(three|see|thee|tree)/ bounces back and forth between matching “I think those are thin trees”.- Put simplest (most efficient) expression first.
- For example, a complicated expression like
/\w+_\d{2,4}|\d{4}_export|export_\d{2}/
- A better way would be
/export_\d{2}|\d{4}_export|\w+_\d{2,4}/