CODEWITHSUNDEEP
regex
jmrah
jmrah

Reputation: 6222

negative lookahead seems to match what it is not supposed to

given the content:

hello bob
hello my name is bob

I am trying to match hello bob using a negative lookahead. The regex hello.*(?!my name is).*bob matches both lines. The regex hello .*(?!my name is) .*bob matches the second line.

How can I match just the first line, and why on earth does the negative lookahead match the line that it's supposed to NOT match against? What am I doing wrong?

Upvotes: 0

Views: 41

Answers (2)

user1019830
user1019830

Reputation:

Using negative lookahead is overkill if you only need to match the first thing, so this regex should be enough:

^hello bob$

Using the start of line anchor (^) and the end of line anchor ($), only hello bob will satisfy that regex.

Upvotes: 1

Allen Luce
Allen Luce

Reputation: 8389

The greedy .* before the negative lookahead is what's keeping it from working correctly. This does the match you're looking for:

/hello (?!my name is).*bob/

Alternatively, you can put the .* into the negative assertion directly:

/hello(?!.*my name is).*bob/

That'll keep the two from competing.

Upvotes: 1

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