The tail command in Linux is used to display the last part of a file or a stream. It is a simple yet powerful tool that allows you to view the end of a file without having to load the entire file into memory. The name “tail” comes from the concept of looking at the “tail end” or the last part of something.

The tail command is commonly used to monitor log files in real-time, as it can continuously display new lines that are added to the end of a file. It is also useful for quickly checking the last few lines of a file or extracting specific lines from the end of a file.

The tail command is available on most Unix-like operating systems, including Linux, macOS, and BSD. It is a standard utility that is included in the GNU Core Utilities package, which is installed by default on most Linux distributions.

Official page of tail package: https://www.gnu.org/software/coreutils/manual/html_node/tail-invocation.html

The tail command is written in C programming language, which is known for its efficiency and low-level system access. The use of C allows the tail command to be fast and lightweight, making it suitable for handling large files and streams.

Installation on Supported Operating Systems

The tail command is typically pre-installed on most Linux distributions. To check if it is already installed, you can open a terminal and run the following command:

tail --version

If the tail command is not found or you need to install it on your system, you can use the package manager specific to your distribution to install it. Here are the commands for some popular Linux distributions:

Ubuntu/Debian:

sudo apt-get install coreutils

CentOS/Fedora:

sudo yum install coreutils

Arch Linux:

sudo pacman -S coreutils

After installing the coreutils package, the tail command should be available for use.

Usage and Examples

The basic syntax of the tail command is:

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

Here are some commonly used options and examples:

Display the last 10 lines of a file:

tail file.txt

This command will display the last 10 lines of the file “file.txt”. If the file has fewer than 10 lines, it will display all the lines.

Display a specific number of lines:

tail -n 5 file.txt

This command will display the last 5 lines of the file “file.txt”. You can change the number to any desired value.

Display lines in real-time:

tail -f file.txt

This command will display the last 10 lines of the file “file.txt” and continuously update the output as new lines are added to the file. It is commonly used to monitor log files in real-time.

Display lines in reverse order:

tail -r file.txt

This command will display the last 10 lines of the file “file.txt” in reverse order. It can be useful for quickly viewing the oldest lines in a file.

Similar Commands and Benefits

There are several other commands and tools that serve a similar purpose to the tail command:

head:

The head command is the counterpart to tail and is used to display the first part of a file or a stream. It can be used to extract the first few lines of a file or to preview the contents of a file.

less:

The less command is a pager utility that allows you to view the contents of a file or a stream in a scrollable manner. It is similar to tail in that it can display the last part of a file, but it also provides additional features such as searching and navigation.

grep:

The grep command is used to search for specific patterns or lines in a file or a stream. It can be combined with tail to extract specific lines from the end of a file that match a certain pattern.

The tail command is a versatile tool that can be used in various scenarios. It is commonly used by system administrators, developers, and analysts to monitor log files, track real-time changes, and extract relevant information from large files.

Scripts Examples

Here are three examples of scripts that utilize the tail command for automation:

Script 1: Monitor Apache Access Logs

#!/bin/bash

tail -f /var/log/apache2/access.log | grep "404"

This script continuously monitors the Apache access log file and filters out lines that contain the string “404”. It can be used to track 404 errors in real-time.

Script 2: Check Disk Space Usage

#!/bin/bash

tail -n 5 /var/log/syslog | grep "disk space"

This script displays the last 5 lines of the system log file and filters out lines that contain the string “disk space”. It can be used to check for disk space warnings or errors.

Script 3: Monitor Application Logs

#!/bin/bash

tail -f /var/log/application.log | awk '/ERROR/ { print $0 }'

This script continuously monitors the application log file and prints out lines that contain the string “ERROR”. It can be used to track errors or exceptions in real-time.

List of Possible Functions and Constants

Function/Constant	Description
-n, --lines=K	Display the last K lines of the file
-f, --follow	Output appended data as the file grows
-r, --reverse	Display lines in reverse order
--help	Display help information
--version	Display version information

Conclusion

The tail command is a powerful tool for viewing the last part of a file or a stream in Linux. It is widely used by system administrators, developers, and analysts to monitor log files, track real-time changes, and extract relevant information from large files. The tail command is fast, efficient, and versatile, making it an essential tool in the Linux command-line arsenal.

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