$_ = "1234567890";
tr [357]
   [888]cd;
print $_, $/;
# prints 357

$_ = join '', map chr(), 0 .. 0x1f;
tr [\3\5\7]
   [\10\10\10]cd;
print join('', map sprintf("\\%o",ord), split //), $/;
# prints \10\10\10\3\5\7