Bash Basics & Syntax – Variables, Quoting, Arrays & Prompt Navigation

Introduction – Build Your Foundation with Bash Syntax

Mastering Bash begins with understanding its core syntax—how commands are structured, how variables work, and how to handle data with arrays and substitutions. This knowledge forms the backbone of writing reliable and flexible Bash scripts.

In this guide, you’ll learn:

• How to use and export shell variables
• What special variables like $?, $0, and $@ do
• How Bash treats single quotes vs double quotes
• How to substitute commands and assign outputs
• How to work with arrays and key-value pairs
• How to navigate and interact with the shell prompt

Topics Covered

Bash: Prompt & Navigation

The Bash prompt (PS1) lets you interact with the shell.

pwd          # Print current working directory
cd /home     # Change directory
ls -l        # List directory contents
history      # Show command history
!!           # Repeat last command

Use Tab for autocomplete and Ctrl + R for reverse history search.

Bash: Using Variables ($var, export, unset)

Assign & Access:

name="Raspberry Pi"
echo $name

Export for Subshells:

export PI_USER="pi"

Unset:

unset name

No spaces around = when assigning.

Bash: Special Variables ($?, $#, $@, $0, $1…)

Use "${@}" in quotes to preserve whitespace.

Bash: Quoting Mechanisms (‘, “, \)

Single Quotes ':

Preserve literal value (no expansion):

echo '$USER'   # prints $USER

Double Quotes ":

Allow variable and command expansion:

echo "User is $USER"

Backslash \:

Escape individual characters:

echo \$HOME

Use quotes properly to handle spaces, variables, and special characters safely.

Bash: Shell Substitutions ($(…), …)

Syntax:

today=$(date)
echo "Today is $today"

Legacy Format (not recommended):

echo "Now is `date`"

Use $(command) for modern, nested-safe scripting.

Bash: Arrays & Associative Arrays

Indexed Array:

arr=(apple banana cherry)
echo ${arr[1]}       # banana
echo ${#arr[@]}      # 3

Looping Through:

for item in "${arr[@]}"; do
  echo $item
done

Associative Array (key-value):

declare -A capitals
capitals[India]="Delhi"
capitals[France]="Paris"
echo ${capitals[France]}

Use declare -A to create associative arrays before assigning.

Summary – Bash Basics & Syntax

Understanding Bash’s syntax unlocks the ability to automate tasks, process user input, and build reusable scripts. Whether you’re creating system tools or automation pipelines, Bash syntax mastery is key.

Key Takeaways:

• Use export to pass variables to child processes
• Special variables like $0, $?, and $@ give you runtime metadata
• Quoting determines how Bash interprets values
• Use $(…) for command output substitution
• Arrays and associative arrays help manage structured data

Real-World Applications:

• Scripting command-line tools
• Configuring startup and environment variables
• Managing argument-driven shell automation
• Processing lists and key-value configurations

FAQ: Bash Basics & Syntax

What’s the difference between $* and $@?
$@ treats quoted arguments individually; $* joins them into one string.

How do I export a variable globally?
Use export var=value. It’s available to child processes of the shell.

Can I nest command substitutions?
Yes:

echo "Today is $(date +%A)"

What’s the best way to store multiple values in Bash?
Use arrays:

arr=(one two three)