1 while s/^(\d*)0\n\1.$/$1/mg || s/^(\d*)\n\1.*$/$1/mg;
[download]

There's a reason I put [1] there instead of your ".". Consider what happens when you have the following:

10010
100100
100101
[download]

The last two lines will be merged, creating

10010
10010
[download]

And your code will strip that final 0 from both lines, creating "1001". Wrong. You must ensure that it's a 1. Can't be "any".

-- Randal L. Schwartz, Perl hacker