tac command in Linux with Examples
Last Updated :
27 Sep, 2024
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.
tac command in Linux – FAQs
What is the difference between tac and cat in Linux?
The cat command prints file contents in order, while tac prints file contents in reverse order (last line first).
Can I use tac to reverse a file based on a custom delimiter?
Yes, you can use the -s option to specify a custom delimiter, such as a comma, space, or any other character.
How do I reverse multiple files using tac?
You can provide multiple filenames as arguments to tac, and it will reverse the contents of each file in the order they are provided:
tac file1.txt file2.txt
Can tac be used with regular expressions?
Yes, by using the -r option, you can treat the separator as a regular expression.
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