I have the following regex pattern to find an email address in my code:

/[\._a-zA-Z0-9-] @[\._a-zA-Z0-9-]{8,}/i

I want to make sure it does not match a certain string if it includes:

abc
xyz

Just to exclude the abc I have tried:

/(?!.*abc)[\._a-zA-Z0-9-] @[\._a-zA-Z0-9-]{8,}/i

But that is horribly slow.

CodePudding user response：

You need to "anchor" the regex to a position that can be found by the regex engine in an optimal way. The best way is to "tie" it to a word boundary position, and that should work here since emails start with word chars:

/\b(?!\S*abc)[\w.-] @[\w.-]{8,}/i

BTW, [_a-zA-Z0-9] is equal to \w in JavaScript regex. Details:

• \b - a word boundary
• (?!\S*abc) - a negative lookahead that fails the match if there are zero or more non-whitespace chars and then abc immediately to the right of the current location
• [\w.-] - one or more word, . or - chars
• @ - a @ char
• [\w.-]{8,}- eight or more word, . or - chars.