Bash-Beginners-Guide

6.3.4. User defined variables
Bash Guide for Beginners
Apart from the built-in variables, you can define your own. When awk encounters a reference to a variable
which does not exist (which is not predefined), the variable is created and initialized to a null string. For all
subsequent references, the value of the variable is whatever value was assigned last. Variables can be a string
or a numeric value. Content of input fields can also be assigned to variables.
Values can be assigned directly using the = operator, or you can use the current value of the variable in
combination with other operators:
kelly@octarine ~> cat revenues
20021009 20021013 consultancy BigComp 2500
20021015 20021020 training EduComp 2000
20021112 20021123 appdev SmartComp 10000
20021204 20021215 training EduComp 5000
kelly@octarine ~> cat total.awk
{ total=total + $5 }
{ print "Send bill for " $5 " dollar to " $4 }
END { print "---------------------------------\nTotal revenue: " total }
kelly@octarine ~> awk -f total.awk test
Send bill for 2500 dollar to BigComp
Send bill for 2000 dollar to EduComp
Send bill for 10000 dollar to SmartComp
Send bill for 5000 dollar to EduComp
---------------------------------
Total revenue: 19500
kelly@octarine ~>
C-like shorthands like VAR+= value are also accepted.
6.3.5. More examples
The example from Section 5.3.2 becomes much easier when we use an awk script:
kelly@octarine ~/html> cat make-html-from-text.awk
BEGIN { print "\nAwk-generated HTML\n
{ print $0 }
END { print "\n\n" }
And the command to execute is also much more straightforward when using awk instead of sed:
kelly@octarine ~/html> awk -f make-html-from-text.awk testfile > file.html
Awk examples on your system
We refer again to the directory containing the initscripts on your system. Enter a command similar to the
following to see more practical examples of the widely spread usage of the awk command:
grep awk /etc/init.d/*
Chapter 6. The GNU awk programming language 76