Create Script Assertion for functional testing

I want to do functional testing of webservice using assertion(scripted) which give custom output as

objective:
Invoke script from command line to test 1 service 1 operation with assertion – (Success we need to log the time taken to a standard performance log file each service , operation and environment should have a unique perf log file) (Failure case we need to display the response and error on the screen)

I want script for the same.