Yes ! It's true. You can invoke or consume or call a Web Service from inside a Linux/Unix shell script. This is same as doing from java or php or .net client. Actually most simple to call or invoke a web service is through shell scripting.
Let’s consider a REST web service that adds two numbers. Also you need to pass a token (string or numeric) as a parameter (consider this as a example - do not think over it as a functionality )