my( $state, $prev, @match )= ( "no foo" );
foreach my $tok (  split /(foo|tarbar|bar)/, $string  ) {
    if(  "foo" eq $tok  ) {
        $state= "foo";   next;
    } elsif(  "tarbar" eq $tok  ) {
        if(  "other" eq $state  ) {
            push @match, $prev;
            # and/or do other stuff here
        }
    } elsif(  "bar" ne $tok  &&  "foo" eq $state  ) {
        $prev= $tok;   $state= "other";   next;
    }
    $state= "no foo";
}