#These two just exit after this command
$result = `ssh-copy-id -i $path_publick_key $user\@$server 2>/dev/null < "$password"`;
$result = `ssh-copy-id -i $path_publick_key $user\@$server 2>/dev/null < "$password\n"`;

#This gives a password prompt, without me printing the $result, which makes me think, that ssh is using some named output device, instead of stdout.
#$result is empty:
$result = `echo "$password"|ssh-copy-id -i $path_publick_key $user\@$server 2>/dev/null`;

##</code><code>##

use IPC::Cmd qw{run};

$ssh_cp_id = '';
$ssh_cp_id_result = run(
	'command'=>"ssh-copy-id -i $path_pk $user\@$server 2>/dev/null",
	'buffer'=>\$ssh_cp_id
);
if($ssh_cp_id_result){
	#print has no effect, as the password prompt got already displayed without being captured to the $ssh_cp_id:
	print $ssh_cp_id;
}