regex to detect specific words

Question

How to match specific words that are not part of a word?

For example, I'd like the regex to detect the three "on" but not the one in "long".

on long on abc the on

When I use (?: |^)the|on|of(?: |$), it detects the "on" in "long" as well which is not what I am looking for.

Use this regex : `/\Won\W/`. Basicaly, you want a non-word character, 'on', then a non-word character — Seblor, May 31 '18 at 12:57
Thanks. This does not catch the first and last "on", though. — Ted, May 31 '18 at 13:36
My bad, this one should work : `/\bon\b/` the `\b` are used to catch word boundaries — Seblor, May 31 '18 at 13:40

score 4 · Accepted Answer · answered May 31 '18 at 13:50

4

There are two things here to mention:

When you want to restrict a context for a group of words, always group them
To match as a whole word, you need to use word boundaries, \b

So, you need

\b(?:the|on|of)\b

See this regex demo.

You can see on the diagram that the word boundaries now pertain to all the alternatives listed with | operator due to the fact they are all enclosed with a non-capturing group.

answered May 31 '18 at 13:50

Wiktor Stribiżew

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Thanks for the explanation, it makes sense :) – Ted May 31 '18 at 14:11
1

Done. :) Thanks again for the help. – Ted May 31 '18 at 14:13
Could I ask you another question related to this? I am trying to group several of the matching words into a named group. For example, given `the on lol on the of`, I am looking for group A = `the on` and group B = `on the of`. I tried something like `(P(\b(?:the|on|of)\b)*) lol (P(\b(?:the|on|of)\b)*)` but it does not work.. :-/ – Ted Jun 05 '18 at 15:17
@Ted You should match whitespace chars between words, see [this demo](https://regex101.com/r/4zAMXw/2). – Wiktor Stribiżew Jun 05 '18 at 17:32

score 1 · Answer 2 · answered May 31 '18 at 13:42

1

You can use this regex :

/\bon\b/

The \b tokens are matching any word boundaries, would they be spaces, string start or end, etc...

So this is pretty straight forward : you need the word on, surrounded by word boundaries.

answered May 31 '18 at 13:42

Seblor

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regex to detect specific words

2 Answers2