sub num2ord {
  local $_ = shift;
#          1        2         3         4
# 1234567890123**789012345678901234567890
  $_.((0,st,nd,rd)[/1?.$/g]||th)
}
[download]

Those ** should be 456, not 46 - that appears to have been copied by everyone ;)

Also, one extra character can be removed:

sub num2ord {
  local $_ = shift;
#          1         2         3
# 123456789012345678901234567890
  $_.=(0,st,nd,rd)[/1?.$/g]||th
}
[download]