Allow only domain names/ips in text string

[yaMz]

I am trying to implement what I call private uploads. Basically, users can check a box to indicate they want their file "private"

 

If so, the upload location is then (exampled as): _domain_/private-folder/$randomfolder

 

Upon uploading their file, the random folder is created, their file moved to the directory, the upload information stored to the database, .htaccess file is created like so:

 

 

info to add to new .htaccess:

Code: [select]

<files "*.*">

Deny from All

</files>

 

<files "*.*">

Allow from

$domains

</files>

 

the string $domains is the domains they enter each seperated by a new line in a form textarea.

 

The problem - how can I make sure this is safe. i.e. I want the string to be obviously proofed with php so that no matter what they input, only domains will be outputted.

 

I need the perfect regular expression set to ensure .htaccess for their folder will only contain domains and end on that note.