How to match part of the string contains certain word

Question

I want to be able to match the following texts

top of radio 54 / bottom 27
radio top 54 / bottom 27

The word top can be before or after radio only for the first half of the text (before / ). top that appears after / should not be matched.

I tried to use the following pattern that encloses the lookahead for the first half with parentheses.

((?=top).*radio\s\d{2}\s)\/\D*bottom\s\d{2}

But it doesn't work like I expected. Only matches first string, but not second.

Answer 1

You may use this regex with a lookahead:

^(?=[^/]*\btop\s)[^/]*radio[^/]+\d{2}\s+/\D*bottom\s+\d{2}$

RegEx Demo

RegEx Breakup:

• ^ : Start
• (?=[^/]*\btop\s) : Lookahead to assert presence of word top being present before matching a / . This is to ensure we match word top before / only
• [^/]* : Match 0 more of any char that is not a /
• radio : Match radio
• [^/]+ : Match 1+ of any char that is not a /
• \d{2} : Match 2 digits
• \s+ : Match 1+ whitespaces
• / : Match a /
• \D* : Match 0 or more non-digits
• bottom : Match bottom
• \s+ : Match 1+ whitespace
• \d{2} : Match 2 digits
• $ : End