---
title: nl — Number lines
date: 2026-10-20
time: 12:00
model: admin
category: programs
author_type: human
summary: Prints a text file with line numbers added.
tags: program, Basic Linux commands, nl
---

Prints a text file with line numbers added.

## Basic Information

| Command Name | nl |
| --- | --- |
| One-line Introduction | Prints a text file with line numbers added. |
| Provided by | GNU coreutils |
| Official Documentation | https://man7.org/linux/man-pages/man1/nl.1.html |
| Supported Operating Systems | Linux, macOS, BSD, WSL |
| Installation Status | Installed by default |
| Category | Linux basic commands (tags: Linux basic commands (tags: nl, line number, numbering, cat)) |

## What is this command?

nl prints input with line numbers. It resembles cat -n but gives finer control over blank lines and number formatting.

-b selects which lines are numbered, -w sets the field width and -s the separator. It is useful when quoting code with line references.

## What problems does it solve?

- Quoting code or configuration with line numbers
- Referring to a specific log line
- Numbering only non-empty lines
- Controlling number width and separator
## Key features

### Numbering

Adds a sequential number before each line.

- **When to use**: Citing documents or code
- **What you get**: You can reference exact lines.
- **Limitations**: The original file is not modified.
### Blank line control

-b a or -b t selects all or non-empty lines.

- **When to use**: Reviewing files with many blank lines
- **What you get**: Numbering stays contiguous and readable.
- **Limitations**: By default only non-empty lines are numbered.
### Formatting

-w and -s change width and separator.

- **When to use**: Producing a consistent output format
- **What you get**: Output stays aligned.
- **Limitations**: The options can feel numerous at first.
## Installation and usage

### Check whether it is installed

```
nl --version
```

sudo apt install coreutils   # Debian/Ubuntu
sudo dnf install coreutils   # Fedora

## Real-world examples

### Basic numbering

Number non-empty lines.

```
nl config.yml | head
```

### Number all lines

Number blank lines too.

```
nl -b a notes.txt | head
```

### Custom format

Change width and separator.

```
nl -w 3 -s ': ' app.py | sed -n '1,10p'
```

---
Source (HTML): https://games.aidebatehub.com/programs/linux/basics/nl.html
This file is an auto-generated Markdown twin of the DevHub document.