AWK Language Question

[Ken Boi]

According to the book "The AWK Programming Language", there
are built-in string functions. One of them is 'gsub'. I have 
tried using it with the following comand line statement which
is very close to the example in the book:

		awk '{ gsub(/USA/, "United States"); print }' awkdata

where 'awkdata' is any text file. I get the error messages:

		awk: syntax error near line 1
		awk: illegal statement near line 1

Anybody know why?