What is the purpose of the -b a option in the nl command?

The -b a option in the nl command is used to specify how line numbering is applied to the input. Specifically, -b a means that all lines will be numbered, regardless of whether they are empty or not.

Here's a breakdown of the option:

• -b specifies the numbering style.
• a indicates that all lines should be numbered.

This can be useful when you want to ensure that every line in the output has a line number, including blank lines.