Linux Terminal Command: tac

The tac command is an essential tool in File Manipulation & Viewing. In this tutorial, we will explore what tac does, look at everyday examples, and cover advanced options to supercharge your command-line workflow.

Concept & Explanation

The tac command is the reverse of cat. It reads files and prints their lines in reverse order (bottom line first, top line last).

Common Options & Syntax

tac [options] [arguments]

Here are the most common flags used with tac:

Simple Usage: Basic default commands.
Detailed View: Shows diagnostic information.
Advanced Actions: Can chain parameters for scripting.

1. Interactive Example (Simple)

Here is how most people run the command:

# Example
tac logs.txt

What it does: Prints the lines of ’logs.txt’ in reverse order.

2. Power-User Example (Advanced)

For scripting and advanced diagnostics, use this configuration:

# Advanced
tac system.log | grep -m 10 'ERROR'

What it does: Reads system logs starting from the bottom (newest logs) and pipes them to grep to find only the first 10 occurrences of ‘ERROR’.

⚙️ Warning & Common Pitfalls

[!WARNING] Because tac must parse lines from the bottom, it buffer-reads files and can be slow on extremely large archives.

Here are some related posts on cli_tty1 you might want to check out:

cat : Concatenate files and print on the standard output.
last : Show listing of last logged in users.
top : Display Linux processes in real time.