less — Linux basic command

Linux / Basic Linux commands / less.html

An interactive viewer for navigating long files page by page. Supports reverse navigation.

Basic Information

What is this command?

less is an interactive viewer that allows you to view long files page by page. Unlike cat, it doesn't load the entire file into memory, only reading the necessary parts, so it can open very large files quickly.

It provides rich features such as forward/backward navigation, search, and moving to specific lines, and you can exit at any time with the q key.

What problem does it solve?

• Check long log files page by page.
• View very large files without memory overhead.
• Search for specific keywords within a file.
• Navigate backwards from the end of the file.

Main features

Page-by-page navigation

Navigate to the next page with the spacebar, and to the previous page with the b key.

• Usage scenario: When reading long files in order.
• Result obtained: You can read page by page without scrolling.
• Limitations: Key inputs may not be familiar to beginners.

Keyword search

Search with / key and move to the next result with n key.

• Usage scenario: When looking for specific errors or keywords in logs.
• Result obtained: You can quickly find the desired location.
• Limitations: Case sensitivity may apply, so caution is needed.

Reverse navigation

You can move upwards (to previous) with the b key or arrow keys.

• Usage scenario: When reading from the end of a file and need to go back upwards.
• Result obtained: Bidirectional navigation is possible.
• Limitations: Movement may be slow in very large files.

Real-time refresh (F key)

Pressing the F key tracks the end of the file in real-time, similar to tail -f.

• Usage scenario: When monitoring logs being recorded in real-time.
• Result obtained: When the file is updated, it is automatically displayed.
• Limitations: You need to press q to return to normal mode.

Installation and execution

Check pre-installation

Included by default in almost all Linux distributions.

which less
less --version

Installation (lightweight environment)

May only need installation in lightweight distributions.

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

Actual usage examples

Basic file opening

View files page by page.

# Open file
less /var/log/syslog

# Basic operations:
# Spacebar: next page
# b: previous page
# /keyword: search
# q: exit

Keyword search

Search for specific content within a file.

# Open file
less /var/log/nginx/access.log

# Execute search
/error          # Search for 'error'
# n: move to next result
# N: move to previous result

# Case-insensitive search
# less -i filename

Real-time log tracking

Monitor the end of the file in real-time.

# Open file
less /var/log/syslog

# Press F key for real-time tracking mode
# (same as tail -f)

# To return to normal mode, press Ctrl+C