Using nl to number lines

This weeks tip shows you how to use nl to add line numbers to a file. One of the more common commands to add line numbers is simply cat -n. However, nl adds extra functionality (such as controlling for white space, zero padding, and column justification).

To use nl with its default options, type nl filename. This will output the file with line numbers to standard out. Empty lines will be skipped by default.

Code Listing 1: Example Usage

// basic use 
% nl filename 
 
// Include empty lines 
% nl -ba filename 
 
// Left justified number column 
% nl -nln filename

For more information on using nl see man nl or info nl.

From http://www.gentoo.org/news/en/gwn/20040119-newsletter.xml