How to Use the Tail Command in Linux

The tail command stands for “tail of the file,” and as the name suggests, it’s primarily used to view the last part of files. Whether you’re monitoring log files or tracking real-time data changes, tail is your go-to utility.

The command is often used in conjunction with other Linux commands like grep for searching, awk for text processing, and | (pipe) for chaining multiple commands together. For example, you might use tail -f /var/log/syslog | grep "error" to monitor system logs for errors in real-time.

General syntax for tail command:

$ tail [OPTION...] [FILE...]

1. Display the exact number of lines

tail -n [number] [file]

Using this option allows you to get the tail command to produce output that will display a certain number of lines in a file.

Example:

Suppose you have a text file named example.txt with the following content:

Line 1: This is the first line.
Line 2: This is the second line.
Line 3: This is the third line.
Line 4: This is the fourth line.
Line 5: This is the fifth line.
Line 6: This is the sixth line.
Line 7: This is the seventh line.
Line 8: This is the eighth line.
Line 9: This is the ninth line.
Line 10: This is the tenth line.

If you want to display the last 3 lines of this file, you would use the following command:

tail -n 3 example.txt

This will show you the last 3 lines of the example.txt file.

Line 8: This is the eighth line.
Line 9: This is the ninth line.
Line 10: This is the tenth line.

2. Display lines starting from a specific line number

tail +[number] [file]

The command with the + sign outputs data starting from the specified line number.

Example:

Let’s say you have a text file named example.txt with the following content:

Line 1: This is the first line.
Line 2: This is the second line.
Line 3: This is the third line.
Line 4: This is the fourth line.
Line 5: This is the fifth line.
Line 6: This is the sixth line.
Line 7: This is the seventh line.
Line 8: This is the eighth line.
Line 9: This is the ninth line.
Line 10: This is the tenth line.

If you want to display the content starting from line 5 to the end of the file, you can use the following command:

tail +5 example.txt

The output will be:

Line 5: This is the fifth line.
Line 6: This is the sixth line.
Line 7: This is the seventh line.
Line 8: This is the eighth line.
Line 9: This is the ninth line.
Line 10: This is the tenth line.

3. Display multiple files

tail [file1] [file2]

Use this command to display the data of multiple files at the same time.

Example 1: Viewing the Last 10 Lines of a Single File

Let’s say you have a file named example.txt with the following content:

Line 1: Hello
Line 2: World
Line 3: This
Line 4: is
Line 5: a
Line 6: sample
Line 7: text
Line 8: file
Line 9: for
Line 10: demonstration
Line 11: purposes
Line 12: only

Running the command:

tail example.txt

Will output:

Line 3: This
Line 4: is
Line 5: a
Line 6: sample
Line 7: text
Line 8: file
Line 9: for
Line 10: demonstration
Line 11: purposes
Line 12: only

Example 2: Viewing the Last 10 Lines of Multiple Files

Suppose you have another file named example2.txt with the following content:

Line 1: Another
Line 2: Example
Line 3: File

You can view the last 10 lines of both example.txt and example2.txt by running:

tail example.txt example2.txt

This will output:

==> example.txt <==
Line 3: This
Line 4: is
Line 5: a
Line 6: sample
Line 7: text
Line 8: file
Line 9: for
Line 10: demonstration
Line 11: purposes
Line 12: only

==> example2.txt <==
Line 1: Another
Line 2: Example
Line 3: File

The ==> <== notation is used to separate the output from different files.

4. Output a certain number of bytes

tail -c [bytes] [file]

To display a specific number of bytes in a text file, use the -c option.

Example:

Let's say we have a file named sample.txt with the following content:

This is the first line.
This is the second line.
This is the third line.
This is the fourth line.
This is the fifth line.

If we want to display the last 20 bytes of this file, we would use the following command:

tail -c 20 sample.txt

5. Use multiple commands at once

tail [file] | [other_command]

Use the tail command with pipes | to use it in conjunction with another command.

Example: Using tail with grep

Let's say you have a log file called server.log and you want to check the last 10 lines for any occurrences of the word "error".

tail server.log | grep 'error'

Here's what happens:

• tail server.log reads the last 10 lines of the server.log file.
• The output is then piped (|) to the grep 'error' command.
• grep 'error' filters the lines to only show those that contain the word "error".

6. Monitor files in real-time

tail -f [file]

The -f option is used to track file changes. When new log entries are added to the log file, it updates the display in the terminal window.

Example:

Let's say you have a log file named application.log that is being written to while an application is running. You want to monitor this log file for any new entries.

Open a Terminal Window, navigate to the directory where application.log is located, i.e cd /path/to/directory.

Run the tail -f command:

tail -f application.log

After running this command, you'll see the last 10 lines of application.log displayed in the terminal. The terminal will stay open, and any new lines added to application.log will be displayed in real-time.

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