Now the guys have explained why your code is failing, you might also consider using:

my $shop =  m/.{8}(\d{4})/ ? $1 : '0000';
[download]

or if you have an aversion to the ternary operator

my $shop = '0000';
$shop = $1 if $AResp =~ /.{8}(\d{4})/;
[download]