Hi Ram,
Since, its for variable you can simply you OOB variable validation regex that comes for URL.
Look for Service Catalog >> Catalog Variables >> Variable Valdiation Regex from application navigator & Then check if an entry exists for URL. If not create one as below.
Regex: (((ftp|http|https):\/\/)|(www\.))([-\w\.\/#$\?=+@&%_:;]+)
Now, go the the variable & then in the Type specification tab select the Regex as created above.
