refers to <Linux Command Line and Shell Scripting Bible>

date:Sep 18 2016

Gawk is to run scripts,So called program.It is programming-like environment.

first example:

$0 represents the entire line of the text.

Each data field is determined in a text line by a field separation character.When gawk reads a line of text,it delineates each data field using the defined field separation character.The default field separation character in gawk is any whitespace character(such as the tab or space characters).

Gawk program on linux