Suppressing Command History in Different Shells

Introduction

In the world of Linux and Unix-like systems, the command-line interface (CLI) is an essential tool for users and administrators. One of the features of the CLI is the ability to keep a history of executed commands. However, there are instances where you might want to suppress certain commands from being logged in history, such as when dealing with sensitive information. This blog post explores how different shells handle command history suppression, particularly for commands preceded by a space.

Bash

Bash, one of the most common shells, does not ignore commands that start with a space by default. To enable this feature, you need to set the HISTCONTROL environment variable to ignorespace or ignoreboth. The latter also ignores duplicated commands. This can be done by adding export HISTCONTROL=ignoreboth to your ~/.bashrc file and reloading it.

Z Shell (ZSH)

Zsh, popular for its customization features, does not ignore space-prefixed commands by default. To enable this, you must set the HIST_IGNORE_SPACE option in your ~/.zshrc file. After adding setopt HIST_IGNORE_SPACE and reloading the .zshrc file, Zsh will start ignoring commands that begin with a space.

Fish Shell

Fish shell is unique in this aspect. It ignores commands starting with a space by default. This built-in behavior makes Fish an outlier, as it requires no additional configuration for this feature.

Other Shells

Shells like Korn Shell (KSH) and C Shell (CSH) do not have a default behavior to ignore space-prefixed commands, nor do they offer a straightforward built-in option to enable such behavior.

Which Shell?

To identify which shell you are using, especially in distributions like Kali Linux, you can use the command echo $0 or echo $SHELL. The former shows the name of the current shell, while the latter displays the path to the default shell executable.

Conclusion

Understanding how different shells handle command history suppression is crucial, especially for cybersecurity experts and system administrators dealing with sensitive information. While Bash and Zsh require configuration to enable this feature, Fish shell offers it by default. Knowing how to activate or utilize this feature can be a significant aspect of maintaining operational security and privacy in a command-line environment.