What a Shell is?

So what actually the Shell is?

The Shell is the “program” that runs on the server side that provides the command-line interface between the user and the operating system.

It’s the program that reads, interprets and run the commands that you type when you connect to a server.

The shell interprets the commands you enter and some of them are “executed” by the shell itself, and others are passed to the operating system to be executed by a program.

Different shells exist — some are mostly historical, while others are still widely used today. The most common ones are bash and zsh. zsh is especially popular among power users and developers 😉

On Linux, every user can choose which shell they want to use as their default login shell.

We can check our current shell with:

echo $SHELL

You can also see the default login shell of your user by checking the content of the file /etc/passwd

grep "^$USER" /etc/passwd

To change your default shell (only for your user):

chsh -s /path/to/shell

For example (-s = set shell and the change applies on next login))

chsh -s /bin/zsh

This file lists all valid login shells on the system

cat /etc/shells

If you’re root 🔐, you can change the shell for another user with:

sudo chsh -s /bin/bash carlos

or edit directly the /etc/passwd (not recommended unless you’re sure what your doing!)

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🧠 Why are there different shells?

Because over time, developers built new shells with more features, better scripting, customization, performance, or user experience — just like how web browsers or text editors evolved.

Each shell aims to:

• Improve on limitations of older shells
• Add scripting capabilities
• Provide better interactivity (autocomplete, colors, plugins, etc.)
• Cater to specific use cases (like scripting vs. interactive use)

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List of the most commonly used shells What Happens When You Connect to a Server via SSH and Run a Command?