HTML input must contain a specific string

I have a input field, which will record the response of the end-user. Say the label of it is Linkedin URL. The user who has to enter the linkedin URL could enter some other input(facebook.com/satyaram2k14), which is not invalid. So how can one check, if the url entered contains string 'linkedin.com' along with other text. Final url should be 'linkedin.com/satyaram2k14'. How can I check for this pattern at front-end.