execute .sql script using powershell and store the output in .sql file

I’m trying to run the sql script .sql file from powershell and save the result into .sql file. Overview : SQL database restore requires a user and permission backup pre-restore and once the restore is complete we need to execute the output( users permissions backup which we did pre-restore ) on the database.

here’s my script and when i execute i see an empty file.

Add-PSSnapin SqlServerProviderSnapin100;
$server = 'DBA_Test';
$database = 'Test';
$mydata = invoke-sqlcmd -inputfile "C:\users\security.sql" -serverinstance $server -database $database | Format-Table -HideTableHeaders -AutoSize
$mydata | out-file C:\users\output.sql;
Remove-PSSnapin SqlServerCmdletSnapin100;

Can someone help me on this ?

Thanks in advance