I have a problem trying to get a certain match to work with negative look behind example @list = qw( apple banana cherry); $comb_tlist = join ("|", @tlist); $string1 = "include $(dir)/apple"; $string2 = "#include $(dir)/apple"; if( string1 =~ /^(?<!#).*($comb_tlist)/) #matching regex I tried, works The array holds a set of variables that is matched against the string. I need the regex to match $string1, but not $string2. It matches $string1, but it ALSO matches $string2. Can anyone tell me what I am attempting wrong here. Thanks!