Add regex to lines in text file if it isn't already present

I'm trying to add regex to the beginning of each line in a text file if it isn't already present. The input is a list of urls and the regex is a list of protocols.

I've tried different if/else loops and cmdlets like add-content/set-content to add the regex but the logic is off each time. Currently what I have is:

$content = Get-Content "C:\path\to\file\test.txt"
$pattern = "[regex]::^(http:\/\/www\.|https:\/\/www\.|http:\/\/|https:\/\/|tcp:\/\/|ssl:\/\/)" 
ForEach-Object { 
    if ($content -match $pattern) 
        {$content}
    else {
        {foreach($_ in $content) {"^(http:\/\/www\.|https:\/\/www\.|http:\/\/|https:\/\/|tcp:\/\/|ssl:\/\/)" + $_ }}
          }
 } | Out-File "C:\path\to\file\test.txt"

I'd like the output to be
^(http://www.|https://www.|http://|https://|tcp://|ssl://)netflix.com ^(http://www.|https://www.|http://|https://|tcp://|ssl://)google.com ^(http://www.|https://www.|http://|https://|tcp://|ssl://)yahoo.com

but the actual output is
"^(http://www.|https://www.|http://|https://|tcp://|ssl://)" + $_