>perl -wMstrict -le
"my %replace = (
   '111' => 'bar',  '1111' => 'world',  '333' => 'perl',
   );
 my $find = join '|', reverse sort keys %replace;
 ;;
 my $str = 'f111,f1111,f333';
 $str =~ s{ f ($find) }{$replace{$1}}xmsg;
 print qq{'$str'};
"
'bar,world,perl'