nl command in Linux with examples

The nl command in Linux is an abbreviation for number lines. If you’ve ever had a large text document and needed to add line numbers to it, the nl command is your saving grace. Rather than going through the painstaking process of numbering each line manually, or importing your text document into a GUI text editor, you can simply use nl from the command line and be done in a matter of seconds.

Just like pretty much any other command on a Linux system, nl is very versatile and supports a wide array of various formatting options. So, it’s easy to get your documents numbered with lines exactly the way you want. You’ll just need to know a few options that you can use with the command.

In this tutorial, you’ll learn how to use the nl command in Linux through examples. Follow along below to learn about the various options that you can use with this command.

In this tutorial you will learn:

• How to use the nl command on Linux

Software Requirements and Linux Command Line Conventions

Category	Requirements, Conventions or Software Version Used
System	Any Linux distro
Software	nl
Other	Privileged access to your Linux system as root or via the sudo command.
Conventions	# – requires given linux commands to be executed with root privileges either directly as a root user or by use of sudo command $ – requires given linux commands to be executed as a regular non-privileged user

Frequently Used Options

The nl command will add sequential numbers to all or some of the lines in a file. Sound simple? Well, it is once you know the syntax. In the examples below, we will go over some of the most frequently used options with the command. This will show you how to adapt the command options depending on the formatting of your file.

As a simple example, we’ve created a text document that contains ten different names of common Linux distributions (one per line). With the nl command, we will show you how to add line numbers to this text document.

nl command in Linux Basic and Advanced Examples

1. To add line numbers to a file, simply pass the name of the file to the nl command. By default, line numbers will be added to every line in the file. See the output below as an example.

   $ nl distros.txt 
        1	AlmaLinux
        2	Arch Linux
        3	CentOS
        4	Debian
        5	Fedora
        6	Gentoo
        7	Manjaro
        8	openSUSE
        9	Red Hat
       10	Ubuntu
   

   This is pretty handy already, but notice that by default, the output adds a tab character and then a line number, and then finally the text itself. This is a great way to quickly see what line a certain string of data appears on. But it may not be so useful in some other situations. You’ll see below how to change the formatting of this output.

2. Let’s try changing the formatting a little. One common way to format line numbers is to put a period after the number. To do so with the nl command, we’ll use the -s option. We will also specify ". ", to indicate that we want the line number to be proceeded by a dot and a space.

   $ nl -s ". " distros.txt 
        1. AlmaLinux
        2. Arch Linux
        3. CentOS
        4. Debian
        5. Fedora
        6. Gentoo
        7. Manjaro
        8. openSUSE
        9. Red Hat
       10. Ubuntu
   

3. What if we want to manipulate the space that precedes the line number? This can be done with the -w (width) option. To get rid of the space entirely, we’ll specify a width of 1. Note that we are still using the -s option from the previous example, which will combine both formatting changes.

   $ nl -w 1 -s ". " distros.txt 
   1. AlmaLinux
   2. Arch Linux
   3. CentOS
   4. Debian
   5. Fedora
   6. Gentoo
   7. Manjaro
   8. openSUSE
   9. Red Hat
   10. Ubuntu
   

4. By default, the nl command won’t number blank lines. In other words, only lines with text on them will be numbered. If you need to number blank lines as well, that can be done with the -b a option.

   $ nl -b a distros.txt 
        1	AlmaLinux
        2	Arch Linux
        3	CentOS
        4	Debian
        5	Fedora
        6	
        7	
        8	Gentoo
        9	Manjaro
       10	openSUSE
       11	Red Hat
       12	Ubuntu
   

5. If you would like to start numbering at some number other than 1, you can use the -v option with nl and specify some other number. As an example, we will start numbering the lines at 100.

   $ nl -v 100  distros.txt 
      100	AlmaLinux
      101	Arch Linux
      102	CentOS
      103	Debian
      104	Fedora
      105	Gentoo
      106	Manjaro
      107	openSUSE
      108	Red Hat
      109	Ubuntu
   

6. To include leading zeros for each line, you can use the -n rz option with nl.

   $ nl -n rz distros.txt 
   000001	AlmaLinux
   000002	Arch Linux
   000003	CentOS
   000004	Debian
   000005	Fedora
   000006	Gentoo
   000007	Manjaro
   000008	openSUSE
   000009	Red Hat
   000010	Ubuntu
   

There are, of course, many more options and styles that you can use with the nl command. It would be very redundant to cover them all here, since there are so many slight variations. We recommend that you use some of the options covered in this guide and add your own tweaks to the command in order to get the formatting exactly as you want with your line numbers.

Closing Thoughts

In this tutorial, we learned all about the nl command on Linux. The nl command is useful when you need to add line numbers to a file. Regardless of how your file is formatted or what kind of requirements you have with your line numbering, we’ve given you all the options you will need with the nl command in Linux.