Regex for finding matching on one part of a String and not another part

Question

(appendCsrfToken).+(\.do\?\w)
matches on a String like...
document.forms[0].action = appendCsrfToken("search.do?lname=Smith");

What I would like to do is find Strings that have the .do? portion but don't have the appendCsrfToken portion. For instance...
document.forms[0].action = "search.do?lname=Smith";

I thought that the following would negation would work but I'm getting no matches when I test it
(^appendCsrfToken).+(\.do\?\w)

How do I properly negate the appendCsrfToken to get the match I'm looking for?

Martin Ender · Accepted Answer · 2013-08-27 18:05:22Z

4

Using ^ for negation only works in character classes. You need a lookahead. The easiest way is to look from the beginning of the string (^) all the way through for appendCsrfToken with a negated lookahead. If that works, then go ahead and match the do?:

^(?!.*appendCsrfToken).*(\.do\?\w)

Demo.

answered Aug 27, 2013 at 18:05

Martin Ender

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2 Comments

Zack Macomber Over a year ago

Yes indeed - that does the trick - what I don't quite understand is the ^(?! portion. Does the article you link explain this (I haven't yet read it)?

Martin Ender Over a year ago

@ZackMacomber yes, that's why I linked it ^^. The ^ and the (?!...) are unrelated. ^ (outside of a character class) is an anchor that matches only at the beginning of the string (without consuming any characters). The (?!...) is a negative lookahead, which fails if its subpattern matches - but doesn't actually consume what's matched by the subpattern... hence it looks ahead. But the article explains this much better than I ever could.

CodeHelp · Accepted Answer · 2013-08-29 01:38:16Z

0

You can also use negative lookbehind. Here's the solution

^(?<!.*appendCsrfToken).*(\\.do\\?\\w)

answered Aug 29, 2013 at 1:38

CodeHelp

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