Using ~~ inchworm secret operator saves a stroke:

          #1234567890123456789012
perl -wle "print~~map{1..<>}2..<>"
[download]

Update: The inchworm secret operator is more clearly described here. I remember it from good old TPR0 way back in 2002. You can read all about TPR0 and the other early Perl golf tournaments by downloading Terje/mtv's excellent Book of Perl Golf.

Relaxing the first line restriction allows 20 strokes (which can probably be further shortened):

         #12345678901234567890
perl -pe "$.>1&$_>0and$\+=$_}{"
[download]

This time we use the }{ eskimo greeting secret operator in harness with Eugene's infamous $\ trick.