How to match part of the string contains certain word

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.

>Solution :

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