Question

I’m terrible with RegEx and found this bit somewhere on the interwebs. It’s for matching Twitter-style @username but it has one small problem – it also accepts a space as a word.

NSRegularExpression *atRegex = [NSRegularExpression regularExpressionWithPattern:@"(?<!\\w)@([\\w\\._-]+)?" options:NSRegularExpressionCaseInsensitive error:&error];

Example: “@erik” is matched correctly, but “@ erik” is also matched and should not be.

Answer 1

Your regular expression contains

@(...)?

The ? at the end means that everything inside the preceding (...) is completely optional. So, your regex doesn’t have to match anything following a @.

To fix this, you may be able to remove the ( )?, leaving:

"(?<!\\w)@[\\w\\._-]+"

However, you should also investigate what that (?<!\\w) is doing for you and whether you need it.