perl -wle '@r=({k=>"r"},{k=>"s"},{k=>"t"});print $_->{k} for sort { $_->{k} cmp $_->{k} } @r'
Use of uninitialized value in string comparison (cmp) at -e line 1.
Use of uninitialized value in string comparison (cmp) at -e line 1.
Use of uninitialized value in string comparison (cmp) at -e line 1.
Use of uninitialized value in string comparison (cmp) at -e line 1.
Use of uninitialized value in string comparison (cmp) at -e line 1.
Use of uninitialized value in string comparison (cmp) at -e line 1.
r
s
t