Backticks only capture STDOUT, not STDERR. For that, you can look at various approaches for capturing STDERR in perlfaq8 or use IPC::Open3.

However, I often recommend IPC::Run3 instead, as it's portable and makes things easy. This will capture both STDOUT and STDERR to the $output variable.

use IPC::Run3;

my $output;
run3("unzip -P $password $zipfile", undef, \$output, \$output);
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