Menu
What does it mean to use a regular expression backtracking?
Also, could you provide an example of this?
255
The \1 in a regex like (a)[\1b] is either an error or a needlessly escaped literal 1. In JavaScript it's an octal escape.
The search() method searches through a string looking for the first location where the regular expression pattern produces a match, and return a corresponding match object.
If your regular expression has named capturing groups, then you should use named backreferences to them in the replacement text. The regex (?' name'group) has one group called “name”. You can reference this group with ${name} in the JGsoft applications, Delphi, .
A question mark ( ? ) immediately following a character means match zero or one instance of this character . This means that the regex Great!? will match Great or Great! .
Backreferences and backtracking are two different things. The former is using the results of a capture later in code, e.g.
(['"]).*?\1 This will match a single- or double-quoted string (ignoring escapes for the moment). It uses a backreference to refer to the open symbol (the single or double quote) so it can match that at the end.
Backtracking, on the other hand, is what regular expressions do naturally during the course of matching when a match fails. For example, if I'm matching the expression
.+b against the string
aaaaaabcd then it will first match aaaaaabc on the .+ and compare b against the remaining d. This fails, so it backtracks a bit and matches aaaaaab for the .+ and then compares the final b against the c. This fails too, so it backtracks again and tries aaaaaa for the .+ and the matches the b against the b and succeeds.
117
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
