A fairly easy option would be to create a csv file of the contacts, upload that csv to your C5 directory and then create a single page to import the contacts.
The single page shows nothing only reads the csv file and create new users using the following function: $newUserInfoObject = UserInfo::add($data);
Where $data is an array that can contain
- uName - the username. Required.
- uEmail - Email address. Required.
- uPassword - the non-encrypted password.
- uIsValidated - Whether the email address has been validated. If not specified, -1 will be saved.
- uIsFullRecord - Set to 1 unless set in the array to 0.
source: C5 users
(you should check if the username already exists, and if so add an incrementing integer to the username)
After you coded the single page to read the csv and added it in the dashboard (back-end), you go to the page once and your contacts will be imported.
How to create a single page: C5 single pages
After importing the data, delete the single page from the system, so no one else can accidently import the same contacts again.