Write a regular expression to match lines not containing a word

David Y.

The Problem

How can I write a regular expression to match lines not containing a specific word?

The Solution

You can do this using a negative lookahead assertion. The PCRE regular expression below will match any line that does not contain the word “word”:

/^((?!word).)*$/gm

Here’s what it does:

  • /: Start regular expression.
  • ^: Match the beginning of a line.
  • (: Start capture group 1.
  • (?!word): Negative lookahead assertion. If “word” is found, discard the current match, otherwise continue evaluating the expression.
  • .: Match any character.
  • ): End capture group 1.
  • *: Match 0 or more of capture group 1.
  • $: Match the end of the line.
  • /: End regular expression
  • g: Global flag. Find all matches in the string, not just the first one.
  • m: Multiline flag. Use ^ and $ to match the start and end of a line, rather than the start and end of the whole string.

Notably, this expression will not match empty lines. If this behavior is desired, we can add the s (dotall) flag, which will make . match all characters including newlines:

/^((?!word).)*$/gms

If the s flag is not supported by your regex implementation, you can replace . with [\s\S] (\s matches whitespace characters, and \S matches everything except whitespace characters).

/^((?!word)[\s\S])*$/gm

Loved by over 4 million developers and more than 90,000 organizations worldwide, Sentry provides code-level observability to many of the world’s best-known companies like Disney, Peloton, Cloudflare, Eventbrite, Slack, Supercell, and Rockstar Games. Each month we process billions of exceptions from the most popular products on the internet.

Share on Twitter
Bookmark this page
Ask a questionJoin the discussion

Related Answers

A better experience for your users. An easier life for your developers.

    TwitterGitHubDribbbleLinkedinDiscord
© 2024 • Sentry is a registered Trademark
of Functional Software, Inc.