less command in Linux with Examples

The less command in Linux is used to view the contents of a file one page at a time without opening it in an editor, making it ideal for reading large files efficiently.

• It allows you to scroll forward and backward through a file.
• It does not load the entire file into memory, making it faster for large files.
• You can search for specific text within the file using /pattern.
• It provides navigation shortcuts (e.g., Space for next page, b for previous page, q to quit).
• Commonly used to view log files, configuration files, or command outputs (cat filename | less or less filename)

Using 'less' with Pipelines

The less command can also be used in conjunction with other commands through pipelines. This allows us to view the output of a command directly in the less pager.

Note: I'm using dmesg output as input to less command in the following examples. 

For Example: If you want to read the contents of dmesg command, it's better to use it with fewer command  

dmesg | less

Output:  

Syntax:

less [options] filename

• Here, `filename` represents the name of the file we want to view using the `less` command.
• The less command provides several options that modify its behavior. Here are some commonly used options:

Examples of `less` command in Linux

Let's look at a few examples to illustrate the usage of the less command with different options.

1. Searching for a pattern

dmesg | less -p "fail"

The above command tells less to start at first occurrence of pattern "fail" in the file and displaying the file from that point.

Output:  

2. Displaying line number

dmesg | less -N

The -N option displays line numbers along with the file content, allowing you to reference specific lines easily.

Output:

3. Checking a small file

less -F /home/Mandeep/test/first.erl

In this example, the file `/home//Mandeep/test/first.erl` is small enough to fit on a single screen. The `-F` option causes less to exit immediately without displaying the file since it can be fully shown in one go.

Commonly Used Options in`less`command

Here are the most commonly used and practical options of the less command in Linux:

Suggested Quiz

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5 Questions

Which command is best for viewing large files page-by-page without opening an editor?

• A

  cat

• B

  nano

• C

  less

• D

  tail

Explanation:

less displays files one page at a time and is optimized for large files.

What happens when you press the Spacebar while using the less command?

• A

  Goes to the start of the file

• B

  Scrolls one page forward

• C

  Quits the viewer

• D

  Searches for a pattern

Explanation:

Spacebar in less moves the view ahead by one page.

Which less option starts displaying the file from the first match of a given pattern?

• A

  less -i pattern

• B

  less -p pattern

• C

  less -s pattern

• D

  less -g pattern

Explanation:

The -p option jumps directly to the first occurrence of the pattern.

What does the command dmesg | less do?

• A

  Filters dmesg logs

• B

  Opens dmesg in an editor

• C

  Sends dmesg output into less for scrollable viewing

• D

  Stores dmesg output in a file

Explanation:

The pipe | sends command output to less so it can be viewed page-by-page.

Which option causes less to quit immediately if the file fits on a single screen?

• A

  -E

• B

  -F

• C

  -n

• D

  -s

Explanation:

The -F flag exits automatically if the entire content fits on one page.

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