I came up with a need in a regular expression for finding numbers that do not start with COM. I tried the following expression, but it does not work as expected, and the condition for COM does not work.
(?!(COM|СОМ))\d{11,19}
1 Answers
You need a negative lookbehind to check if a string is not immediately preceded with some other pattern. Also, since you are matching a range of digits, you should include digit boundaries, (?<!\d) and (?!\d), to your regex.
Use
(?<!COM|\d)\d{11,19}(?!\d)
(?<!COM)(?<!\d)\d{11,19}(?!\d)
See the regex demo. The latter will work with Python and Boost regex libraries that require the lookbehind alternatives to match the text of the same length.
Details
(?<!COM)- a negative lookbehind that fails the match if there isCOMimmediately to the left of the current location(?<!\d)- a negative lookbehind that fails the match if there is as digit immediately to the left of the current location\d{11,19}- eleven to nineteen digits(?!\d)- a negative lookahead that fails the match if there is as digit immediately to the right of the current location.
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