As we uncover the section of Awk features, in this part of the series, we shall walk through the concept of built-in variables in Awk. There are two types of variables you can use in Awk, these are; user-defined variables, which we covered in Part 8 and built-in variables.
You will realize that, the filename is printed out for each input line, that is the default behavior of Awk when you use `FILENAME` built-in variable.
Using `NR` to count the number of lines (records) in an input file, remember that, it also counts the empty lines, as we shall see in the example below.
When we view the file domains.txt using cat command, it contains 14 lines with text and empty 2 lines:
Next, you can also specify an input field separator using the FS built-in variable, it defines how Awk divides input lines into fields.
The default value for FS is space and tab, but we can change the value of FS to any character that will instruct Awk to divide input lines accordingly.
There are two methods to do this:
- one method is to use the FS built-in variable
- and the second is to invoke the -F Awk option
Consider the file /etc/passwd on a Linux system, the fields in this file are divided using the : character, so we can specify it as the new input field separator when we want to filter out certain fields as in the following examples:
To specify an output field separator, use the OFS built-in variable, it defines how the output fields will be separated using the character we use as in the example below:
In this Part 10, we have explored the idea of using Awk built-in variables which come with predefined values. But we can also change these values, though, it is not recommended to do so unless you know what you are doing, with adequate understanding.
After this, we shall progress to cover how we can use shell variables in Awk command operations, therefore, stay connected to Tecmint.
