tac command in Linux with Examples

tac command in Linux is used to concatenate and print files in reverse. This command will write each FILE to standard output, the last line first. When no file is specified then this command will read the standard input.

Here, we will look deeper into the tac command, exploring its syntax, various options, and practical use cases to help you master this command and boost your productivity in Linux environments.

Syntax

tac [OPTION]... [FILE]...

where,

• [OPTION]: Additional options that modify the behavior of the command (more details below).
• [FILE]: One or more files to process. If no file is specified, tac reads from standard input.

Basic Example

Let’s explore a basic example of how the tac command works.

tac tacexample.txt

It will print files in reverse.

Key Options for the tac Command

The tac command comes with several options to modify its behavior, providing additional functionality and control over how it processes files.

1. tac -b: Attach the Separator Before

The -b option attaches the separator before the line. This option is useful when working with files that have specific delimiter requirements.

Example:

tac -b concat.txt tacexample.txt

2. tac -r: Interpret the Separator as a Regular Expression

The -r option treats the separator as a regular expression, allowing for more advanced pattern matching.

Example:

tac -r concat.txt tacexample.txt

3. tac -s: Use STRING as the Separator Instead of Newline

The -s option allows you to specify a custom string as the separator. This is particularly useful when working with CSV files or other formats that use custom delimiters.

Example:

tac -s concat.txt tacexample.txt

4. tac --help: Display Help Text

This option displays a brief help text, showing all available options and how to use them.

Example:

tac --help

5. tac --version: Display Version Information

To check the current version of the tac command installed on your system, use the --version option.

tac --version

Conclusion

The tac command in Linux is a simple yet highly effective tool for reversing the content of files. Whether you're analyzing logs, processing CSV files, or working with large datasets, mastering tac can help you work more efficiently. By understanding the available options and combining tac with other Linux utilities, you can unlock its full potential for a wide range of use cases.