Introduction to Shells

A shell is a command-line interface that allows users to interact with the operating system. It serves as a bridge between the user and the system kernel, enabling command execution, scripting, and automation.

Shell	Description	Common OS
Bash (bash)	Most widely used, default on many Linux distros	Linux/macOS (older)
Zsh (zsh)	More advanced than Bash, customizable	macOS (default since Catalina), Linux
Fish (fish)	User-friendly, auto-suggestions, colorful UI	Linux/macOS
PowerShell (pwsh)	Object-oriented, designed for Windows	Windows
Command Prompt (cmd)	Basic Windows shell	Windows

Types of ShellsGetting Started with a Shell

Checking Your Current Shell

Run:

echo $SHELL

This returns something like /bin/bash or /bin/zsh.

Opening a Shell

Linux/macOS: Open Terminal (Ctrl + Alt + T on Linux, Cmd + Space -> Terminal on macOS).
Windows: Open Command Prompt (cmd), PowerShell, or WSL (for Linux-based shells).

Basic Shell Commands

Command	Description
pwd	Print current directory
ls	List files in a directory
cd <directory>	Change directory
mkdir <name>	Create a new directory
rm <file>	Remove a file
rmdir <dir>	Remove an empty directory
touch <file>	Create an empty file
cp <src> <dest>	Copy files
mv <src> <dest>	Move/Rename files
cat <file>	View file content
echo "Hello"	Print output
whoami	Show current user
exit	Close the shell

Shell Scripting Basics

A Shell script is a file containing a series of commands.

Creating a Simple Script

Create a new file:nano myscript.sh

Add the following:
 #!/bin/bash

echo "Hello, World!"

Save and exit (Ctrl + X, then Y, then Enter).

Make the script executable: chmod +x myscript.sh

Run it:./myscript.sh

Working with Variables

#!/bin/bash

name="Deepak"

echo "Hello, $name!"

Conditional Statements

#!/bin/bash

if [ $1 -gt 10 ]; then

    echo "Greater than 10"

else

    echo "Less than or equal to 10"

fi

Loops in Shell

For Loop

for i in 1 2 3 4 5; do

    echo "Number: $i"

done

While Loop

count=1

while [ $count -le 5 ]; do

    echo "Count: $count"

    count=$((count+1))

done

Aliases and Shortcuts

To create a shortcut command, add an alias to your ~/.bashrc or ~/.zshrc:

alias ll="ls -lah"

Then apply changes:

source ~/.zshrc

Next Steps

Learn file permissions (chmod, chown)
Understand pipes (|), redirection (>, <, >>)
Explore environment variables (export VAR=value)
Use functions in scripts

Shell Basics Guide