Bash Shell Guide

Bash (Bourne Again Shell) is the default shell on most Linux distributions and macOS. It’s a powerful, feature-rich shell that’s perfect for both interactive use and scripting.

Key Features

Interactive Use

Command history with arrow keys
Tab completion for commands, files, and arguments
Job control (foreground/background processes)
Aliases and functions

Scripting

Full programming language features
String manipulation
Arrays
Conditionals and loops

Installation

macOS (default, but outdated)

# Install latest via Homebrew
brew install bash
# Add to list of shells
sudo bash -c 'echo /opt/homebrew/bin/bash >> /etc/shells'
# Set as default
chsh -s /opt/homebrew/bin/bash

Ubuntu/Debian

# Already installed! Just set as default
chsh -s /usr/bin/bash

Configuration Files

File	Purpose
`~/.bashrc`	Run for interactive non-login shells
`~/.bash_profile`	Run for login shells (macOS)
`~/.bash_login`	Run if .bash_profile not found
`~/.profile`	Run for login shells (Ubuntu)
`/etc/bash.bashrc`	System-wide config

Tip: Put interactive configs in ~/.bashrc and login configs in ~/.profile

Common Aliases

# Shortcuts
alias ll='ls -lah'
alias la='ls -A'
alias l='ls -CF'

# Safety
alias rm='rm -i'
alias cp='cp -i'
alias mv='mv -i'

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

# Navigation
alias ..='cd ..'
alias ...='cd ../..'
alias ....='cd ../../..'

Functions

# Function with arguments
function mkcd() {
    mkdir -p "$1" && cd "$1"
}

# Usage: mkcd newproject

# Git functions
function gco() {
    git checkout "$1"
}

# Extract archives
extract() {
    if [ -f "$1" ] ; then
        case "$1" in
            *.tar.bz2) tar xjf "$1" ;;
            *.tar.gz) tar xzf "$1" ;;
            *.bz2) bunzip2 "$1" ;;
            *.rar) unrar x "$1" ;;
            *.gz) gunzip "$1" ;;
            *.tar) tar xf "$1" ;;
            *.tbz2) tar xjf "$1" ;;
            *.tgz) tar xzf "$1" ;;
            *.zip) unzip "$1" ;;
            *.Z) uncompress "$1" ;;
            *.7z) 7z x "$1" ;;
            *) echo "'$1' cannot be extracted" ;;
        esac
    else
        echo "'$1' is not a valid file"
    fi
}

Prompt Customization

Basic PS1 Example

# Add to .bashrc
export PS1='\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '

# Color codes:
# \033[0;30m - Black
# \033[0;31m - Red
# \033[0;32m - Green
# \033[0;33m - Yellow
# \033[0;34m - Blue
# \033[0;35m - Purple
# \033[0;36m - Cyan
# \033[0;37m - White

Git Branch in Prompt

parse_git_branch() {
    git branch 2>/dev/null | grep '*' | sed 's/* //'
}

PS1='\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[01;31m\]$(parse_git_branch)\[\033[00m\]\$ '

Environment Variables

# Add to PATH
export PATH="$HOME/bin:$PATH"

# Editor
export EDITOR=vim
export VISUAL=vim

# History
export HISTSIZE=10000
export HISTFILESIZE=20000
export HISTCONTROL=ignoredups:erasedups

Useful Shortcuts

Shortcut	Action
`Ctrl+A`	Move to beginning of line
`Ctrl+E`	Move to end of line
`Ctrl+U`	Clear line before cursor
`Ctrl+K`	Clear line after cursor
`Ctrl+R`	Search history
`Ctrl+L`	Clear screen
`Ctrl+C`	Cancel current command
`Ctrl+Z`	Suspend/background process
`!!`	Repeat last command
`!$`	Last argument of previous command

Shell Options

# Useful shopt options
shopt -s histappend        # Append to history
shopt -s checkwinsize      # Update window size
shopt -s globstar          # ** for recursive paths
shopt -s nocaseglob        # Case-insensitive globbing

# Add to .bashrc to make permanent

Conditionals

# Basic if
if [ -f "$file" ]; then
    echo "File exists"
fi

# If-else
if [ $# -eq 0 ]; then
    echo "No arguments"
else
    echo "Arguments: $@"
fi

# String comparisons
if [ "$var" = "hello" ]; then
    echo "Hello!"
fi

# Numeric comparisons
if [ $num -gt 10 ]; then
    echo "Greater than 10"
fi

Loops

# For loop over files
for file in *.txt; do
    echo "Processing $file"
done

# For loop over command output
for i in $(seq 1 5); do
    echo "Number $i"
done

# While loop
while read line; do
    echo "$line"
done < file.txt

Tips & Tricks

Colorized output

# Red
echo -e "\033[0;31mThis is red\033[0m"

# Green
echo -e "\033[0;32mThis is green\033[0m"

Check command success

cd /some/directory && echo "Success" || echo "Failed"

Default value

# Use default if variable is empty
echo "${VAR:-default}"