Negative regex for Perl string pattern match

Question

I have this regex:

if($string =~ m/^(Clinton|[^Bush]|Reagan)/i)   {print "$string\n"}; 

I want to match with Clinton and Reagan, but not Bush.

It's not working.

Answer 1

Your regex does not work because [] defines a character class, but what you want is a lookahead:

(?=) - Positive look ahead assertion foo(?=bar) matches foo when followed by bar (?!) - Negative look ahead assertion foo(?!bar) matches foo when not followed by bar (?<=) - Positive look behind assertion (?<=foo)bar matches bar when preceded by foo (?<!) - Negative look behind assertion (?<!foo)bar matches bar when NOT preceded by foo (?>) - Once-only subpatterns (?>\d+)bar Performance enhancing when bar not present (?(x)) - Conditional subpatterns (?(3)foo|fu)bar - Matches foo if 3rd subpattern has matched, fu if not (?#) - Comment (?# Pattern does x y or z) 

So try: (?!bush)

Answer 2

Sample text:

Clinton said
Bush used crayons
Reagan forgot

Just omitting a Bush match:

$ perl -ne 'print if /^(Clinton|Reagan)/' textfile Clinton said Reagan forgot 

Or if you really want to specify:

$ perl -ne 'print if /^(?!Bush)(Clinton|Reagan)/' textfile Clinton said Reagan forgot