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06. Shells & Shell Configurations

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06. Shells & Shell Configurations

Overview¶

A shell is a text-based interface that allows users to interact with the operating system by:

Executing commands
Running programs
Managing files and directories
Controlling permissions and processes

The shell acts as a bridge between the user and the kernel, interpreting commands and returning output.

Accessing the Shell¶

Users interact with the shell through:

Terminal (Linux GUI)
Console (command-line interface)

A command prompt is displayed where commands can be entered.

Check Current Shell¶

echo $SHELL

Example Output¶

/bin/bash

Explanation¶

$SHELL is an environment variable
It shows the default shell assigned to the current user

List Available Shells¶

cat /etc/shells

Example Output¶

/bin/sh
/bin/bash
/usr/bin/zsh
/usr/bin/fish

Explanation¶

Displays all installed shells on the system
Useful when selecting or changing shells

Switching Between Shells (Temporary)¶

bash

sh

dash

Explanation¶

Starts a new shell session
Does not permanently change the default shell

Exit Back¶

exit

Change Default Shell (Permanent)¶

Step 1: Run Command¶

chsh

Step 2: Enter Password¶

Required for authentication

Step 3: Enter Shell Path¶

/bin/bash

Explanation¶

Sets the default login shell
Takes effect after logout/login

Alternative Command¶

chsh -s /bin/bash

Explanation

-s → specify shell directly
Faster method to change shell

Common Shells¶

Shell	Description
`sh`	Basic shell (Bourne Shell)
`bash`	Most widely used shell
`dash`	Lightweight and fast shell
`zsh`	Advanced shell with plugins
`fish`	User-friendly interactive shell

Practical Examples¶

Example 1: Check Current Shell¶

echo $SHELL

Example 2: List Installed Shells¶

cat /etc/shells

Example 3: Switch to Another Shell¶

zsh

Example 4: Change Default Shell¶

chsh -s /usr/bin/zsh

Important Notes¶

Only valid shells listed in /etc/shells can be used
Changes apply after re-login
Root privileges may be required in some cases

Summary Table¶

Command	Purpose
`echo $SHELL`	Show current shell
`cat /etc/shells`	List available shells
`bash`, `sh`, `zsh`	Switch shell temporarily
`chsh`	Change default shell
`chsh -s`	Set shell directly

Conclusion¶

The shell is a core component of Linux that enables:

Command execution
System interaction
Automation through scripting

Understanding how to manage and switch shells improves efficiency and flexibility in Linux environments.