---
layout: page
topic: The nl command
author: Domenico Votta
category_title: Advanced Commands
category_page: Advanced
tags: number lines
title: nl
---
<p>The <code>nl</code>  is a command that permits to number the lines. Through some flags you can decide how to filter this command.</p>
We have a file named <code>example.txt</code> that contains 5 elements, to test this command:
{% highlight ruby linenos %}
Car
Computer
Robot
Smartphone
Videogame
{% endhighlight %}

The syntax command is:
<pre> nl [flags][file] </pre>

{% highlight ruby linenos %}
nl example.txt
 1  Car
 2  Computer
 3  Robot
 4  Smartphone
 5  Videogame
{% endhighlight %}
<p>How you can see the command has numbered the lines.</p>

<h2>Flags</h2>

<p>Here a list that contains the main flags of these command:
<ul>

  <li> <b>-b</b>: Specify the lines to be numered </li>
  {% highlight ruby linenos %}
nl -b p^[cv] example.txt
   1  Car
   2  Computer
   3  Videogame
      Robot
      Smartphone
  {% endhighlight %}
  <p> <code>p^[cv]</code> says to nl to number only the lines that start with c and v.</p>

  <li> -b<b>n</b>: The flag n goes with b, doesn't number any lines </li>
  {% highlight ruby linenos %}
nl -bn example.txt
     Car
     Computer
     Videogame
     Robot
     Smartphone
  {% endhighlight %}

  <li> <b>-s</b>: Usually nl separes the number of the line from the text with a tab, with -s flag you can choose another separator, in this example we will use "=". </li>
  {% highlight ruby linenos %}
nl -s= example.txt
   1=Car
   2=Computer
   3=Videogame
   4=Robot
   5=Smartphone
  {% endhighlight %}

</ul>
</p>