UCC121-1, Session 1: Course Content¶

Topic: Mastering the Shell Environment¶

1. What is a Shell?¶

A shell is a program that provides the user with a direct interface to the operating system. It takes your commands, interprets them, and asks the operating system to perform the requested action.

Interface: It's a Command-Line Interface (CLI).
Role: Sits between you (the user) and the operating system's core (the kernel).
Default Shell: On most Linux systems, the default shell is bash (the Bourne Again SHell).

You can find out what shell you are using with the command: echo $SHELL

2. The `.bashrc` File: Your Personal Toolbox¶

When you start an interactive shell, it automatically runs a script to set up your environment. This script is .bashrc (located in your home directory, ~/.bashrc).

Purpose: To store all your personal customizations: aliases, functions, and environment variables.
Activation: Changes made to .bashrc are not applied automatically to your current session. You must load them by either:
1. Starting a new shell session.
2. Running the command source ~/.bashrc.

3. Aliases: Your Command-Line Shortcuts¶

An alias is a simple way to create a shortcut for a longer command. They are perfect for commands you use often.

Syntax: alias shortcut_name='the_long_command'

Common & Useful Examples:

# Make 'ls' more informative and colorful
alias ls='ls --color=auto'
alias ll='ls -alF'
alias la='ls -A'
alias l='ls -CF'

# Shortcuts for system updates (Debian/Ubuntu)
alias update='sudo apt update && sudo apt upgrade'

# Show open ports
alias ports='netstat -tulpn'

How to add them: Open ~/.bashrc with a text editor (like nano or vim) and add these lines. Then run source ~/.bashrc.

Removing an alias: unalias shortcut_name

4. Functions: Super-Powered Aliases¶

Functions are like aliases, but they are more powerful. They can accept arguments (parameters), contain multiple commands, and use logic.

Syntax:

function_name() {
  # command 1
  # command 2
  # use $1, $2 for arguments
}

Example: The mkcd function

A common task is to create a directory and then immediately navigate into it. - Problem: mkdir new_dir followed by cd new_dir. - Solution: A function that does both!

# Creates a directory and changes into it
mkcd() {
  mkdir -p "$1" && cd "$1"
}

mkdir -p "$1": Creates the directory. -p ensures it doesn't fail if the directory exists and also creates parent directories if needed. "$1" is the first argument you provide to the function.
&&: This is a logical AND. The cd "$1" command only runs if the mkdir command was successful.

5. Environment Variables: The Shell's Memory¶

Environment variables are dynamic values that affect the processes and programs running in the shell. By convention, their names are in uppercase.

Key Variables to Know:

`PATH`¶

What it is: A colon-separated list of directories that the shell searches through when you type a command.
How it works: When you type ls, the shell looks for an executable file named ls in each directory listed in $PATH.
View it: echo $PATH
Modify it: To add a custom scripts folder (e.g., ~/bin) to your PATH, you would add this to .bashrc: export PATH="$HOME/bin:$PATH" This tells the shell to look in~/bin` first, then in all the other standard locations.

`PS1`¶

What it is: The Primary Prompt String. This variable controls what your command prompt looks like.
Customization: You can use special backslash-escaped characters to insert dynamic information.
View it: echo $PS1
Common PS1 codes:
- \u: Username
- \h: Hostname (the computer's name)
- \w: The current working directory
- \t: The current time (HH:MM:SS)
- \$: Displays a # if you are the root user, $ otherwise.

Example PS1 Customization:

# A prompt showing user@host:directory
export PS1='[\u@\h \w]\$ '

# A prompt with colors (this can look complex!)
export PS1='[\033[01;32m\]\u@\h[\033[00m]:[\033[01;34m\]\w[\033[00m]\$ '

6. Lab Exercises (TP/CC)¶

Open ~/.bashrc: Use a text editor like nano ~/.bashrc.
Add Aliases: Add the ll and update aliases shown in the examples above.
Add a Function: Add the mkcd function.
Customize your Prompt: Add the colored PS1 export line from the example.
Activate Changes: Save the file and run source ~/.bashrc.
Test Everything:
- Type ll. Does it show a detailed file listing?
- Type type update. Does it show that update is an alias?
- Use your new mkcd function: mkcd test_directory. Did it create the folder and move you inside it?
- Does your prompt look different and colorful?

UCC121-1: Shells, Scripting, and Data Management¶

Session 1: Mastering the Shell Environment¶

What is a Shell?¶

A program that takes your commands and tells the operating system what to do.

You -> Shell -> OS Kernel -> Hardware

It is your primary interface for controlling the system. We will be using Bash (Bourne Again SHell).

Your Toolbox: `~/.bashrc`¶

An essential configuration file in your home directory.

Purpose: Stores your personal customizations.
Execution: Runs automatically every time you open a new terminal.
Rule: After editing, you must run source ~/.bashrc to apply changes to your current session.

Aliases: Your Command-Line Shortcuts¶

Create short, memorable names for long, complex commands.

Syntax: alias name='long_command'

# Example
alias ll='ls -alF'

Useful Alias Examples¶

# For detailed, human-readable file listing
alias ll='ls -alFh'

# For system updates (Debian/Ubuntu)
alias update='sudo apt update && sudo apt upgrade'

# To quickly show all active network ports
alias ports='netstat -tulpn'

Functions: Super-Powered Aliases¶

For when an alias is not enough.

Can contain multiple commands.
Can accept arguments ($1, $2, etc.).
Can include logic.

Syntax:

function_name() {
  commands
}

Function Example: `mkcd`¶

A common workflow: create a directory, then cd into it.

# Add this to your ~/.bashrc
mkcd() {
  mkdir -p "$1" && cd "$1"
}

Usage: mkcd my_new_project

Environment Variables¶

Dynamic, named values that programs use to configure their behavior.

Conventionally named in UPPERCASE.
View any variable with echo $VARIABLE_NAME.
Set them with export VARIABLE_NAME="value".

The `PATH` Variable¶

How does the shell find commands like ls or grep? It searches the PATH.

$PATH is a colon-separated list of directories.
echo $PATH
To add your own script directory (e.g., ~/bin): export PATH="$HOME/bin:$PATH" (Add this to ~/.bashrc)

The `PS1` Variable: Your Prompt¶

This variable controls what your command prompt looks like.

Special Characters: - \u : Username - \h : Hostname - \w : Current Directory - \$ : $ for normal users, # for root.

Example: export PS1='[\u@\h \w]\$ ' Result: [user@hostname ~]$

Lab Time!¶

Open ~/.bashrc with a text editor.
Add the ll alias.
Add the mkcd function.
Add a custom PS1 variable to make your prompt colorful.
- export PS1='[\033[01;32m\]\u@\h[\033[00m]:[\033[01;34m\]\w[\033[00m]\$ '
Run source ~/.bashrc.
Test that your alias, function, and new prompt all work correctly.

Questions?¶

Next Session: Text Processing Tools: grep, sed, and awk