open in, shift @ARGV; 
for(<in>){
[download]

Obvious?

You will hardly find any example in the perldocs ever trying this.

Rather

open in, shift @ARGV; 
while (<in>){
[download]

or better

open my $in, '<', shift @ARGV; 
while (my $line = <$in>){
[download]

Explanation

your code is semantically equivalent to

my @temp_list=<in>;
for(@temp_list){
[download]

for expects a list and evaluates in list context¹, so it's greedily swallowing all at once.

But while iterates in scalar context, that is line by line (as defined by '$/')

¹) with a little magical exception in recent Perl versions (>= 5.8 ?) regarding ranges, which isn't relevant here