C:\tmp>perl -MO=Deparse -e "$_ =10; my $x = 'a' x 10"
$_ = 10;
my $x = 'aaaaaaaaaa';
-e syntax OK

C:\tmp>perl -MO=Deparse -e "$_ =10; my $x = 'a' x $_"
$_ = 10;
my $x = 'a' x $_;
-e syntax OK

C:\tmp>