Regex for sequence of characters that is not equal to

Question

I have a URL pattern that looks like this: ^foo\/(?P<prefix>[a-z]+)\/bar\/$.

I need the sequence of characters in the middle to be different than another sequence of characters, let's say ab.

foo/somestring/bar/ and foo/abcde/bar/ should match, but foo/ab/bar/ should not.

I've come as far as ^foo\/(?P<prefix>(?!ab)[a-z]+)\/bar\/$, but that doesn't match foo/abcde/bar/.

Wiktor Stribiżew · Accepted Answer · 2016-04-11 18:47:10Z

1

You just forgot about restricting the negative lookahead value until the /:

^foo\/(?P<prefix>(?!ab\/)[a-z]+)\/bar\/$
                      ^^

See the regex demo

If you use (?!ab), it forbids matching values that start with ab. Adding the trailing boundary makes it disallow anything that equals that value inside the negative lookahead.

answered Apr 11, 2016 at 18:47

Wiktor Stribiżew

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