Here's a sub with 62 characters. Expects the number as an argument and returns 1 or 0.

sub luhn {
#2345678901234567890123456789012345678901234567890123456789012
for(pop=~/(.)(.)/g){($a+=$1)+=$_ for map{split//}2*$2}!($a%10)
}
[download]

/prakash