I'm not sure I like the idea of embedding the parameters in a string. Another way might be to make open understand a hashref in place of the filename string, so you can use the old fashioned open FH, "$mode_char$filename" style but optionally write, f.ex open FH, { name => "filename", sequential => 1, mode => "R" }; or something in that vein.

Makeshifts last the longest.