Aha! I forgot that the 1st parameter on setfenv referred to the current function, though how would a 5.2 polyfill cope with it?… My setfenv -reimplementation checks what arg#1 is and if it's a number (=stack level), then it uses debug.getinfo( lvl, "f" ).func as the function. (Plus rather...

Is checking for setfenv enough to discover 5.1? No. Quite a few people define setfenv / getfenv as compatibility functions (or use modules that provide these.) (Not terribly many, but if you do this, it'll probably break for someone eventually.) (OTOH, if you do stuff that doesn't break if someone ...

In that case, can you explain so I don't make this mistake again? (unixoid examples only:) simplified core of that example code: os.execute( table.concat( {command, " \"", old, "\" \"", new, "\""} ) ) or (equally bad but more readable): os.execute( ...