$ (echo 1 ; echo 2 ; echo 3) > 1
$ (echo 1 ; echo 2 ; echo 3 ; echo 4) > 2
$ perl -le'for(@ARGV) { open my $fh, "<", $_; 1 while <$fh>; print $. }' 1 2
3
4
$ perl -le'for(@ARGV) { open my $fh, "<", $_; 1 while <$fh>; print $. }' 2 1
4
3