Comment by cordite
6 years ago
That was a fantastic demonstration of what backtracking meant. Thank you John for your in depth description of what went wrong.
As a follow up, would something like `[^=]=.` be a better capture group regex?
6 years ago
That was a fantastic demonstration of what backtracking meant. Thank you John for your in depth description of what went wrong.
As a follow up, would something like `[^=]=.` be a better capture group regex?
Yes. I think HN stole your asterisks. You meant:
That is, zero or more 'not-equals-sign-characters', followed by an equals sign.
Where the first regex is 57 steps for x=xxxxxxxxxxxxxxxxxxxxxxxx, the second is just 7.
Avoid using greedy .* for backtracking regex engines! Give your greedy regex engine the hints it needs to do what it does best.
Don't use a backtracking regex engine is probably the better lesson. I want a tool that won't unexpectedly poke me with the sharp bit.
The article says that even lazy matches can have catastrophic backtracking.