Building a regex to capture INT., EXT., INT./EXT., etc

True, you need to use lazy dot matching with \w.*?, but you can also optimize the pattern to shorten the alternation group like this:

/^\w.*?(INT\.(?:\/EXT\.)?|EXT\.(?:\/INT\.)?)(.*)$/

See the regex demo

Also, if you are processing the text as a whole, you will need a /m multiline modifer.

Details:

• ^ - start of a string
• \w - a word char
• .*? - any 0+ chars other than line break chars as few as possible up to the first
• (INT\.(?:\/EXT\.)?|EXT\.(?:\/INT\.)?) - Group 1 capturing either:
  • INT\.(?:\/EXT\.)? - INT. followed with optional /EXT. substring
  • | - or
  • EXT\.(?:\/INT\.)? - EXT. followed with optional /INT. substring
• (.*) - Group 2: any 0+ chars other than line break chars up to the...
• $ - end of string.