I would use ^FOO(?!BA[RZ]\b).*$, ie put the \b inside the look-ahead. Otherwise, only 'FOO' is matched.

$ perl -le '/^FOO(?!BA[RZ]\b).*$/ and print for qw/FOOBAR FOOBARS FOOB
+AZ FOOBAZS FOOQUX FOO/'
FOOBARS
FOOBAZS
FOOQUX
FOO

[download]

Update: added example

--
David Serrano

In reply to Re^2: Zero-width look-ahead regexp question by Hue-Bond
in thread Zero-width look-ahead regexp question by rovf

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