The problem seems to be the location of your ()'s. To get the substitution to work correctly, use $string =~ s/([^<B>]($swapString)[^<\/B>])/<B>$1<\/B>/gi; Update:
if you don't want the period and spaces to be bold, use 
$string =~ s/([^<B>])($swapString)([^<\/B>])/$1<B>$2<\/B>$3/gi;

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In reply to Re: Double regex match not working correctly. by dailylemma
in thread Double regex match not working correctly. by the_0ne

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