$ perl -TMScalar::Util=tainted -wE '$x = $0; say tainted $x; ($x) = keys %{{$x => 1}}; say tainted $x'
1
0
$ perl -TMScalar::Util=tainted -wE '$x = $0; say tainted $x; $x = join "", map {chr ord substr $x, $_, 1} 0 .. length($x) - 1; say tainted $x'
1
0
$ perl -TMScalar::Util=tainted -wE '$x = $0; say tainted $x; $x = lc $x; say tainted $x'  # May change the case of $x
1
0
$ perl -TMScalar::Util=tainted -wE '$x = $0; say tainted $x; $x = eval qq["${\quotemeta $x}"] or die; say tainted $x'
1
0