Using ~~ inchworm secret operator saves a stroke:
#1234567890123456789012
perl -wle "print~~map{1..<>}2..<>"
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$\+=$_}{"
This time we use the
}{ eskimo greeting secret operator in harness with Eugene's infamous
$\ trick.