c:\@Work\Perl\monks>perl -wMstrict -le
"my $pattern = qr{ \b f[eio]e \b }xms;
 ;;
 my $str = 'foo bar feeble macfee unfeeling fee fumble';
 ;;
 print qq{match: '$1'} if $str =~ m{ (bar (?: (?! $pattern) .)* f \w+) }xms;
"
match: 'bar feeble macfee unfeeling fee'