I'm looking for a regex that matches words with prefix symbol, say @word, for example, it should match @word in:

it should match @word
@word should be matched
or @word as well
and if it's the last word in a sentence followed by a symbol @word.

But it should not match if it's part of a word, e.g.:

@wordgame should not match
nor check@word

Basically I want to match exact @word as a standalone word (including the prefix).

I first tried:

\b(@word)\b

with word boundaries, it doesn't work because of @.

I also tried the regex in D-E-N's answer:

(^|\W)(@word)\b

It almost works, one minor issue is the \W for non-word characters matches the space in front of the word as well, for example:

this is a @word.

It matches ' @word' with a space before @

What should be the right regex?

Thanks!

CodePudding user response：

Because of your requirements I'm unsure the generic \W\w character classes are what's needed here, it looks like you're using properly formed English sentences.

Regex

(?<=^|\s)@word(?=$|[.\s])

Description

This answer simply checks for the following:

Look-backward for:
- ^: Assert position at the beginning of a line (at beginning of the string or after a line break character) (line feed)
- OR \s: A “whitespace character” (ASCII space, tab, line feed, carriage return, vertical tab, form feed)
Look-forward for:
- The literal character “.”
- OR \s: A “whitespace character” (ASCII space, tab, line feed, carriage return, vertical tab, form feed)

Further expansion

If you say also wanted to allow:

some sentence ending with an exclamation point @word!

Then you would change out [.\s] for [.\s!]

CodePudding user response：

\b is only a short for (^\w|\w$|\W\w|\w\W) (but as zero length). You can take your stuff from this to get the correct data:

(^|\W)(@word)\b

will find @word with a non-word character or line start before (\W^) and word boundary at end (\W or $)

You can test on regex101.com

CodePudding user response：

^@word$ seems to work perfectly for what you are testing. Basically, what this does is:

Ensures that the phrase must start with @, per ^
Ensures that word is in the list
Ensures that there is nothing after word, per $

I was able to prove this out by using: https://regex101.com/

I was also able to prove that the negative cases dont match:

@wordgame
another@word

Hopefully that works for you.