How to Use the tee Command in Linux: Step-by-Step Guide

Understanding the tee Command

• 💡 The tee command in Linux is used to display output on the terminal while simultaneously writing that same output to one or more files.
• 🎯 It's incredibly useful when you need to see command results in real-time and also preserve them for later review.

Basic Usage and Overwriting

• 🚀 To use tee, you typically pipe the output of another command into it, followed by the desired filename (e.g., ls | tee output.txt).
• ⚠️ By default, tee will overwrite the content of the specified file if it already exists.
• 📝 For example, piping echo hello to tee file.txt will result in file.txt containing only 'hello'.

Appending Output with tee -a

• ➕ To append output to a file instead of overwriting it, use the -a option (e.g., echo next line | tee -a file.txt).
• 📄 This ensures that new output is added to the end of the file, preserving previous content.

Writing to Protected System Files with sudo tee

• 🔑 When you need to write to protected system directories (like /etc/), you can use sudo tee.
• ⚙️ The syntax echo test | sudo tee /etc/test.conf allows you to write content to system files after entering your password.

Writing to Multiple Files and Saving Disk Usage

• 🗄️ The tee command can write output to multiple files simultaneously by listing them after the command (e.g., ls | tee file1.txt file2.txt).
• 📊 A practical example is saving disk usage information using df -h | tee disk-usage.txt, which displays the output and saves it to disk-usage.txt.