two arguments with nawk program

Shell Programming and Scripting
1

Can someone help me to understand this part of code?

/bin/nawk -f awkfile file1 file2

I know awkfile is the one with awk script.
file1 is source file that needs to be processed.
What is file2 two?

Thanks for your help!

2 

$ awk '{ print $0 } ' file1
abcd
$ awk '{ print $0 } ' file1 file2
abcd
pqrs
$ cat file1
abcd
$ cat file2
pqrs
3

(n)awk can take multiple files to process.

4

Never mind.
I found FILENAME is sytem variable for awk.

awk FILENAME Current filename.

Thanks!!

5

Can I use a system variable to write an if statement to code
to process two files differently?