$ perl -MO=Deparse -wE "say scalar('a', 'e', 'i', 'o', 'u');"
Useless use of a constant ("a") in void context at -e line 1.
Useless use of a constant ("e") in void context at -e line 1.
Useless use of a constant ("i") in void context at -e line 1.
Useless use of a constant ("o") in void context at -e line 1.
BEGIN { $^W = 1; }
use feature 'current_sub', 'evalbytes', 'fc', 'say', 'state', 'switch', 'unicode_strings', 'unicode_eval';
say scalar('???', '???', '???', '???', 'u');
-e syntax OK