print can be used as follows:

print $SCALAR LIST
print $SCALAR
print BLOCK LIST
print BLOCK
print LIST
print
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You have the following:

print $ads{$this_ad} "$line\n";
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$ads{$this_ad} doesn't match $SCALAR or BLOCK, so this must be print LIST. But that's not what you want. Replace what you have with

print { $ads{$this_ad} } "$line\n";
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or

$ads{$this_ad}->print("$line\n");
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