$ perl -MO=Deparse,-p,-q -E 'my $foo = qq{a_${blah}_b}; my $bar = q{a_} . $blah . q{_b};'
use feature 'current_sub', 'bitwise', 'evalbytes', 'fc', 'postderef_qq', 'say', 'state', 'switch', 'unicode_strings', 'unicode_eval';
(my $foo = 'a_' . $blah . '_b');
(my $bar = 'a_' . $blah . '_b');
-e syntax OK