How to capture unknown number of words in between a negative lookbehind catch term regex?

Question

I am trying to exclude records which have the word "owner" somewhere preceding the word "dog"

• the owner has a dog (exclude)
• the owner has a black and brown dog (exclude)
• John has a dog (include)
• John has a black and brown dog (include)

Here is current regex:

\b(?<!owner\s)\w+\sdog\b

This works for a single unknown word ('owner has dog' is excluded but 'owner has a dog' is included)), however, I am unable to capture multiple words which retain its negative look behind across all words between "owner" and "dog".

Many Thanks

Answer 1

You can use the following regular expression to verify that the string contains the word "dog" that is not preceded by the word "owner".

^(?:(?!\bowner\b).)*\bdog\b

Start your engine! _{^<¯\(ツ)/¯^>} Python code

Python's regex engine performs the following operations.

^                : anchor match to beginning of string
(?:              : begin a non-capture group
  (?!\bowner\b)  : use a negative lookahead to assert that the current
                   position in the string is not followed by "owner"
  .              : match a character
)                : end non-capture group
*                : execute non-capture group 0+ times
\bdog\b          : match 'dog' surrounded by word boundaries

The technique of matching a sequence of individual characters that do not begin an outlawed word is called Tempered Greedy Token Solution.

Answer 2

Another option could be to start matching any char except o or a newline.

Then in case you encounter an o, assert that it is not the word owner followed by matching any char except an o or a newline and optionally repeat that process until you match the word dog.

 ^[^o\r\n]*(?:(?!\bowner\b)o[^o\r\n]*)*\bdog\b

Explanation

• ^ Start of string
• [^o\r\n]* Match 0+ times any char except o or a newline
• (?: Non capture group
  • (?!\bowner\b) Negative lookahead, assert not the word owner directly to the right
  • o[^o\r\n]* Match o followed by 0+ times any char except o or newline
• )* Close non capturing group and repeat 0+ times
• \bdog\b Match the word dog

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