$ perl -E '
    my @x = (
        [qw{P007b_Yum P007_Yum}],
        [qw{P007B_YUM P007_YUM}],
        [qw{P007b_yum P007_yum}]
    ); 
    for (@x) { 
        say $_->[0] for sort { $a->[1] cmp $b->[1] } 
        map { [ $_, lc $_ ] } @$_; 
        say "-" x 3; 
    }
'
P007_Yum
P007b_Yum
---
P007_YUM
P007B_YUM
---
P007_yum
P007b_yum
---