Lesson 17: Shell Configuration

Goal: Customize your terminal with aliases, environment variables, prompt, and shell configuration files.

Table of Contents

1. Shell Types — bash vs zsh
2. Configuration Files
3. Aliases
4. Environment Variables
5. The PATH Variable
6. Prompt Customization (PS1)
7. Useful .bashrc Configuration
8. Exercises

Shell Types — bash vs zsh

Check your current shell

echo $SHELL
# Output: /bin/bash or /bin/zsh

Bash (Bourne Again Shell)

• Default on most Linux distributions
• Stable, well-documented, universal
• Config files: ~/.bashrc, ~/.bash_profile

Zsh (Z Shell)

• Default on macOS, popular on Linux
• Better autocompletion and features
• Config file: ~/.zshrc
• Extensible with Oh My Zsh

Switch shells

# Install zsh
sudo apt install zsh

# Change your default shell
chsh -s /bin/zsh

# Log out and back in for the change to take effect

Configuration Files

Load order for bash

Login shell (SSH, terminal login):
  1. /etc/profile          (system-wide)
  2. ~/.bash_profile       (user, OR ~/.bash_login OR ~/.profile)
  3. ~/.bashrc             (usually sourced from .bash_profile)

Non-login shell (new terminal window):
  1. ~/.bashrc

The key file: ~/.bashrc

# View your bashrc
cat ~/.bashrc

# Edit it
nano ~/.bashrc

# After editing, reload it
source ~/.bashrc
# or shorthand
. ~/.bashrc

Aliases

Aliases create shortcuts for long or common commands.

Create temporary aliases

# Only lasts for current session
alias ll='ls -la'
alias gs='git status'

Create permanent aliases

Add them to ~/.bashrc:

# Open bashrc
nano ~/.bashrc

# Add at the end:
alias ll='ls -la'
alias la='ls -A'
alias l='ls -CF'
alias ..='cd ..'
alias ...='cd ../..'
alias gs='git status'
alias ga='git add .'
alias gc='git commit -m'
alias gp='git push'
alias update='sudo apt update && sudo apt upgrade -y'
alias myip='curl -s ifconfig.me'
alias ports='ss -tulnp'
alias df='df -h'
alias du='du -h'
alias free='free -h'
alias mkdir='mkdir -pv'
alias grep='grep --color=auto'

# Reload
source ~/.bashrc

List and remove aliases

# Show all aliases
alias

# Remove an alias for current session
unalias ll

Aliases with arguments — use functions

Aliases can't take arguments. Use functions instead:

# Add to ~/.bashrc

# Create directory and enter it
mkcd() {
    mkdir -p "$1" && cd "$1"
}

# Quick find
qfind() {
    find . -name "*$1*"
}

# Extract any archive
extract() {
    if [ -f "$1" ]; then
        case "$1" in
            *.tar.bz2) tar xjf "$1" ;;
            *.tar.gz)  tar xzf "$1" ;;
            *.tar.xz)  tar xJf "$1" ;;
            *.bz2)     bunzip2 "$1" ;;
            *.gz)      gunzip "$1" ;;
            *.tar)     tar xf "$1" ;;
            *.zip)     unzip "$1" ;;
            *.7z)      7z x "$1" ;;
            *)         echo "'$1' cannot be extracted" ;;
        esac
    else
        echo "'$1' is not a file"
    fi
}

Environment Variables

View variables

# All environment variables
env

# Specific variable
echo $HOME
echo $USER
echo $SHELL
echo $PATH
echo $EDITOR
echo $LANG

Set variables

# For current session only
export MY_VAR="hello"
echo $MY_VAR

# Permanent — add to ~/.bashrc
echo 'export EDITOR="nano"' >> ~/.bashrc
echo 'export VISUAL="nano"' >> ~/.bashrc
source ~/.bashrc

Common variables to set

# Add to ~/.bashrc

# Default editor
export EDITOR="nano"
export VISUAL="nano"

# Language
export LANG="en_US.UTF-8"

# History settings
export HISTSIZE=10000
export HISTFILESIZE=20000
export HISTCONTROL=ignoreboth:erasedups

# Colored man pages
export LESS_TERMCAP_mb=$'\e[1;32m'
export LESS_TERMCAP_md=$'\e[1;32m'
export LESS_TERMCAP_me=$'\e[0m'
export LESS_TERMCAP_se=$'\e[0m'
export LESS_TERMCAP_so=$'\e[01;33m'
export LESS_TERMCAP_ue=$'\e[0m'
export LESS_TERMCAP_us=$'\e[1;4;31m'

Unset a variable

unset MY_VAR

The PATH Variable

PATH tells the shell where to find executables.

View your PATH

echo $PATH
# Output: /usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin

# Show it nicely
echo $PATH | tr ':' '\n'

How PATH works

When you type ls, the shell searches these directories in order:

1. /usr/local/bin/ls — not found
2. /usr/bin/ls — found! Execute this.

Add to PATH

# Temporary
export PATH="$HOME/bin:$PATH"

# Permanent — add to ~/.bashrc
echo 'export PATH="$HOME/.local/bin:$HOME/bin:$PATH"' >> ~/.bashrc
source ~/.bashrc

Practical: Add custom scripts to PATH

# 1. Create a bin directory
mkdir -p ~/bin

# 2. Create a script
cat > ~/bin/sysinfo << 'EOF'
#!/bin/bash
echo "=== System Info ==="
echo "Host: $(hostname)"
echo "User: $USER"
echo "Date: $(date)"
echo "Uptime: $(uptime -p)"
echo "Memory: $(free -h | awk '/Mem/ {print $3 "/" $2}')"
echo "Disk: $(df -h / | awk 'NR==2 {print $3 "/" $2 " (" $5 ")"}')"
EOF

# 3. Make it executable
chmod +x ~/bin/sysinfo

# 4. Ensure ~/bin is in PATH (add to .bashrc if not)
export PATH="$HOME/bin:$PATH"

# 5. Run from anywhere
sysinfo

Prompt Customization (PS1)

The prompt is controlled by the PS1 variable.

Escape sequences for PS1

Examples

# Simple: user@host:dir$
PS1='\u@\h:\w\$ '

# With colors
PS1='\[\e[1;32m\]\u@\h\[\e[0m\]:\[\e[1;34m\]\w\[\e[0m\]\$ '

# Minimal
PS1='\W \$ '

# With date and time
PS1='[\d \t] \u@\h:\w\$ '

# Two-line prompt
PS1='\[\e[1;32m\]\u@\h\[\e[0m\] \[\e[1;34m\]\w\[\e[0m\]\n\$ '

Make it permanent

# Add to ~/.bashrc
echo "PS1='\[\e[1;32m\]\u@\h\[\e[0m\]:\[\e[1;34m\]\w\[\e[0m\]\$ '" >> ~/.bashrc
source ~/.bashrc

Useful .bashrc Configuration

Here's a complete, well-commented .bashrc addition:

# Append this to your ~/.bashrc

# ─── History ──────────────────────────────────────
HISTSIZE=10000
HISTFILESIZE=20000
HISTCONTROL=ignoreboth:erasedups
shopt -s histappend

# ─── Navigation ──────────────────────────────────
shopt -s cdspell         # autocorrect cd typos
shopt -s autocd          # type directory name to cd into it
shopt -s dirspell        # autocorrect directory names

# ─── Aliases ─────────────────────────────────────
alias ll='ls -la --color=auto'
alias la='ls -A --color=auto'
alias ls='ls --color=auto'
alias ..='cd ..'
alias ...='cd ../..'
alias ....='cd ../../..'
alias grep='grep --color=auto'
alias df='df -h'
alias du='du -h'
alias free='free -h'
alias mkdir='mkdir -pv'

# Git shortcuts
alias gs='git status'
alias ga='git add'
alias gc='git commit -m'
alias gp='git push'
alias gl='git log --oneline -10'
alias gd='git diff'

# System
alias update='sudo apt update && sudo apt upgrade -y'
alias myip='curl -s ifconfig.me && echo'
alias ports='ss -tulnp'

# ─── Functions ───────────────────────────────────
# Create directory and cd into it
mkcd() { mkdir -p "$1" && cd "$1"; }

# Quick backup of a file
bak() { cp "$1" "$1.bak.$(date +%Y%m%d-%H%M%S)"; }

# ─── Prompt ──────────────────────────────────────
PS1='\[\e[1;32m\]\u@\h\[\e[0m\]:\[\e[1;34m\]\w\[\e[0m\]\$ '

# ─── Path ────────────────────────────────────────
export PATH="$HOME/.local/bin:$HOME/bin:$PATH"
export EDITOR="nano"

Apply changes

source ~/.bashrc

Exercises

Exercise 1: Create aliases

# 1. Create a temporary alias
alias hello='echo "Hello, $USER!"'
hello

# 2. Add permanent aliases to .bashrc
echo "alias cls='clear'" >> ~/.bashrc
echo "alias h='history 20'" >> ~/.bashrc
source ~/.bashrc

# 3. Test them
cls
h

Exercise 2: Environment variables

# 1. Set a custom variable
export PROJECT_DIR="$HOME/projects"
echo $PROJECT_DIR

# 2. Check your default editor
echo $EDITOR

# 3. Set nano as default editor (permanent)
echo 'export EDITOR="nano"' >> ~/.bashrc
source ~/.bashrc
echo $EDITOR

Exercise 3: Custom script in PATH

# 1. Create ~/bin
mkdir -p ~/bin

# 2. Create a weather script
cat > ~/bin/weather << 'EOF'
#!/bin/bash
curl -s "wttr.in/${1:-Berlin}?format=3"
EOF
chmod +x ~/bin/weather

# 3. Add to PATH if needed
export PATH="$HOME/bin:$PATH"

# 4. Use it
weather
weather London

Key Takeaways

• ~/.bashrc — your main configuration file
• source ~/.bashrc — reload after changes
• alias name='command' — create shortcuts
• export VAR="value" — set environment variables
• PATH — tells the shell where to find programs
• PS1 — customize your prompt
• Functions for aliases that need arguments
• Always back up .bashrc before major changes: cp ~/.bashrc ~/.bashrc.bak

Next Lesson: Lesson 18: Networking & SSH →