How to add conditional element to regex?

Asked Aug 09 '23 at 20:08

Active Aug 09 '23 at 20:16

Viewed 26 times

Lets say I have this:

< hello!

So I just want to match <.

so I just do <

But what if it does this:

<< hello!

I don't want it to match <, because << is a different regex expression I have (<<).

How do I make it only match < if it is it?

edited Aug 09 '23 at 20:12

Barmar

asked Aug 09 '23 at 20:08

j v

Check out the [`^` assertion](https://stackoverflow.com/a/16944517/5459839) in regex. – trincot Aug 09 '23 at 20:10
@trincot I don't see anything in the question about matching at the beginning of the line. Only if it's not part of `<<`. – Barmar Aug 09 '23 at 20:14
1

use negative lookarounds so you only match `<` if there's no other `<` before or after it. – Barmar Aug 09 '23 at 20:14
use quantifier for that position? `<{1}` – Jorge Campos Aug 09 '23 at 20:15
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@JorgeCampos Did you try it? It will match each of the `<`. – Barmar Aug 09 '23 at 20:16
Added dupe reference for excluding cases where the character to match is repeated. – trincot Aug 09 '23 at 20:16
@Barmar He didn't specify the structure of the sentence or the original regex, he just mentioned that he doesn't want it to match the double `<<` so my suggestion also works. I see your point though. And yes I did test it. https://regex101.com/r/zYrx3q/1 – Jorge Campos Aug 09 '23 at 20:20
@JorgeCampos In your regex101, it matches the second `<` in `<< home`. – Barmar Aug 09 '23 at 20:23
Note also that `{1}` is always redundant. Unless a pattern is quantified, it matches exactly one time. – Barmar Aug 09 '23 at 20:23
@Barmar aah, I see what you mean. Thanks for the input! – Jorge Campos Aug 09 '23 at 21:20

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