Hi there...
Regular Expression for your requirements is :
/(?=^.{8,50}$)(?=(?:.*?\d))(?=.*[a-z])(?=(?:.*?[@#$%}{:;?.]){1})(?!.*\s)/
(?=(?:.*?[@#$%}{:;?.]){1}) : It looks for at least one Special characters like @,#,$,%. You can place other special characters also.
Thanks.