Regex that matches "hello @c" but not "hello @cat"

Question

When trying to parse a string a string for mentions I was using this regex: .*@${username}.* where ${username} is a parameter.

if ${username} = 'c'

then this becomes .*@c.* so this will incorrectly match something like hello @cat.

I need a regex that matches the entire string:

@c
hello @c
@c hello
hello @c hello

and does not match:

@cat

It doesn't have to be one regex. It could be multiple ones that cover all cases without interfering with another case.

This seems to work: `(^|\s)@c(\s|$)`. Probably a bunch of better ways to do it, not a regex guru. — Tibrogargan, Apr 23 '17 at 07:05
Possible duplicate of [Regex match entire words only](http://stackoverflow.com/questions/1751301/regex-match-entire-words-only) — JJJ, Apr 23 '17 at 07:05
@JJJ problem with \b is the `@` character, so it's not the same question — Tibrogargan, Apr 23 '17 at 07:06
@JJJ The answer you linked uses \b (and/or \w) to delimit the term (a word) being searched for, but the problem is that @ is not a word character so there is not boundary before or after it. The term is not a word. — Tibrogargan, Apr 23 '17 at 07:10
@Tibrogargan The OP is interested only in the ending of the word. Surely they have the common sense to adapt the duplicate to their code (`@c\b`). — JJJ, Apr 23 '17 at 07:14
@Tibrogargan I appreciate the effort! JJJ: Thanks! I just learned the term "word boundary" from this. Sorry for duplicate question. — atkayla, Apr 23 '17 at 07:33

score 0 · Answer 1 · answered Apr 23 '17 at 07:06

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Just make sure that the user name is not followed by a username constituant: @$username$[^a-z]\|$$. Note that depending on the regexp parser you might need to remove the backslashes.

answered Apr 23 '17 at 07:06

kmkaplan

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score 0 · Accepted Answer · edited May 23 '17 at 12:02

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This seems to work.

.*@\bc\b.*

https://regex101.com/r/OYjmvQ/1

I was also wondering why it wasn't working in my actual code though (Java) and derp: Java Regex Word Boundaries

had to be double escaped:

.*@\\bc\\b.*

edited May 23 '17 at 12:02

Community

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answered Apr 23 '17 at 07:32

atkayla

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Regex that matches "hello @c" but not "hello @cat"

2 Answers2