How to Run Scripts Without Saving Terminal History

In the world of Linux system administration, maintaining privacy and security while executing commands in the Ubuntu terminal is often a priority. Whether you're running a script to check for software updates or performing sensitive operations, you may want to avoid saving certain commands in the terminal's history. This blog post explores how to execute a script, such as one downloaded via curl, without leaving a trace in the Ubuntu terminal history. We'll walk you through the process in an organized manner, discuss the merits and demerits, and provide essential cautions.

Why Avoid Saving Terminal History?

The terminal history in Ubuntu, stored in the ~/.bash_history file, logs all commands executed in a session. While this is useful for recalling past commands, it can pose risks in certain scenarios:

• Security: Sensitive commands, such as those involving API keys, passwords, or scripts from external sources, could be exposed if the history file is accessed by unauthorized users.

• Privacy: On shared systems, you may not want other users to see the commands you've run.

• Audit Compliance: In production environments, avoiding history logs for specific commands can help meet compliance requirements by reducing the exposure of sensitive operations.

This is particularly critical in production servers, where logging sensitive commands could lead to accidental leaks of proprietary scripts, configuration details, or operational workflows. By preventing these commands from being saved, you reduce the risk of sensitive data being accessed during audits or breaches.

Step-by-Step Guide to Running Scripts Without Saving History

Below is an organized approach to running a script (e.g., curl -sSL <example-script-url> | bash) without saving it in the terminal history. Follow these steps in order:

Step 1: Verify the Script's Safety

Before executing any script, especially one downloaded from the internet, inspect its contents to ensure it’s safe. For example, if you're running a script from https://raw.githubusercontent.com/example/check-update/master/script.sh:

1. Download the Script:
   
   curl -sSL https://raw.githubusercontent.com/example/check-update/master/script.sh > script.sh

2. Inspect the Script:
   
   cat script.sh

Look for malicious code, unexpected network calls, or file modifications. Only proceed if the script is trustworthy.

Step 2: Choose a Method to Avoid History Logging

There are three effective methods to prevent the command from being saved in the terminal history. Choose one based on your needs:

Method 1: Prepend a Space

If the HISTCONTROL environment variable is set to ignorespace or ignoreboth, a command with a leading space won't be saved.

Check HISTCONTROL:

echo $HISTCONTROL

 If it includes ignorespace or ignoreboth, you're ready. If not, set it:

export HISTCONTROL=ignorespace

Run the Script:

curl -sSL https://raw.githubusercontent.com/example/check-update/master/script.sh | bash

•  Note the space before curl. This is the simplest method if HISTCONTROL is configured.
  
  

Method 2: Temporarily Disable History

Disable history logging for the current session, run the script, and re-enable history.

Disable History:

set +o history

Run the Script:

curl -sSL https://raw.githubusercontent.com/example/check-update/master/script.sh | bash

Re-enable History:

set -o history

Method 3: Remove the Command from History

Run the script normally, then delete the specific command from the history.

Run the Script:

curl -sSL https://raw.githubusercontent.com/example/check-update/master/script.sh | bash

Delete the Command:

history -d $(history 1 | awk '{print $1}')

Step 3: Verify the History

After running the script, confirm the command isn’t in the history:

history | tail

If the command is absent, you’ve successfully avoided logging it.

Step 4: Secure the Terminal Session

Clear Temporary Files: If you downloaded the script for inspection, remove it:

rm script.sh

Log Out: If you’re on a shared or production server, log out to ensure no sensitive data remains in the session.

Merits of Avoiding Terminal History

• Enhanced Security: Prevents sensitive commands from being stored in ~/.bash_history, reducing the risk of exposure.

• Privacy Protection: Keeps your commands private on shared systems.

• Compliance: Aligns with security policies that restrict logging sensitive operations in production environments.

• Flexibility: Multiple methods (space prepend, disabling history, or deleting entries) cater to different use cases.

Demerits of Avoiding Terminal History

• Loss of Command Recall: You can’t easily recall the command later for reuse or troubleshooting.

• Potential Oversight: Forgetting to re-enable history (in Method 2) could lead to missing other important commands in the history.

• Complexity: Requires extra steps compared to running commands normally, which may slow down workflows.

Conclusion

Running scripts without saving them in the Ubuntu terminal history is a valuable technique for maintaining security and privacy, especially in production environments. By following the steps outlined—verifying the script, choosing a method to avoid history logging, verifying the history, and securing the session—you can execute commands like curl -sSL <example-script-url> | bash discreetly. The methods provided are simple yet effective, catering to both novice and experienced Linux users.

Caution: Executing scripts directly from the internet (curl | bash) is inherently risky. Always inspect the script’s content and verify its source before running it. Incorrect use of history manipulation commands could also disrupt your workflow or inadvertently expose other commands. Proceed at your own risk and ensure you understand the implications of each method.

By adopting these practices, you can enhance the security of your Ubuntu terminal operations while maintaining control over what gets logged.