The binding operator =~ means that the operation on the right side is applied on the variable on its left side. So your regex is applied to $1, which is empty. Try ($date,) = /^(\d+\/\d+\/\/d+)/; instead.

Maybe you can have a look at the -a switch in perlrun. It splits the input into @F, so your first two fields are in $F[0] and $F[1] (because by default the field separator is ' ').