🐚 Bash Variables – Using $var, export, and unset in Shell Scripts

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🧲 Introduction to Bash Variables – $var, export, and unset Explained

In Bash scripting, variables are a fundamental part of storing, modifying, and passing data throughout a session or script. Whether you’re writing a small script or managing system-wide environment variables, mastering how to declare ($var), export, and unset variables will enhance your control over the Linux shell environment.

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🎯 In this article, you’ll learn:

• How to define and use variables in Bash
• The difference between local and environment variables
• How to export variables to child processes
• How to delete variables with unset
• Best practices and syntax pitfalls

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💡 What Are Variables in Bash?

A variable in Bash is a name that points to a value (usually a string). Bash doesn’t require explicit data types—everything is treated as text unless evaluated.

🔤 Basic Variable Assignment

name="Alice"
echo $name

✅ Output:

Alice

🧠 No spaces around the equal sign (=) in Bash variable assignment!

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🧪 Examples – Declare, Access, and Use Variables

📌 Define and Echo a Variable

greeting="Hello"
echo "$greeting, World!"

📌 Quotes Matter!

message="Welcome to Bash"
echo $message        # Safe if no spaces
echo "$message"      # Best practice

📌 Avoid Common Mistake

# ❌ Incorrect (with space)
title = "Developer"   # Syntax Error

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🌐 Exporting Variables with export

The export command makes a variable available to child processes, like subprocesses or other scripts.

✅ Example:

name="Vaibhav"
export name

🔍 Check Exported Variables:

printenv name
# Output: Vaibhav

⚠️ Variables not exported are only accessible within the current shell/session.

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🧹 Deleting Variables with unset

Use unset to remove a variable from the shell environment.

✅ Example:

age=30
unset age
echo $age
# Output: (blank)

🧠 unset removes both local and exported variables.

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🧠 Local vs Environment Variables

Type	Visibility	Set With	Example
Local Variable	Current shell only	var=value	count=5
Environment Variable	Current shell + subprocesses	export	export path="/bin"

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📋 Variable Naming Rules in Bash

• Must start with a letter or underscore
• Can contain letters, digits, and underscores
• Cannot include spaces or special characters like -
• Are case-sensitive

✅ Valid Examples:

my_name="bash"
_user="root"
MAX_LIMIT=100

❌ Invalid Examples:

2var=5        # starts with digit
my-var=123    # contains hyphen

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📂 Temporary vs Permanent Environment Variables

🔄 Temporary Environment Variables (Current Session Only)

export TEMP_VAR="session"

🔒 Permanent Environment Variables (System/User Level)

Add to:

• ~/.bashrc
• ~/.bash_profile
• /etc/environment (system-wide)

Example:

export JAVA_HOME="/usr/lib/jvm/java-11-openjdk"

Then reload:

source ~/.bashrc

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📌 Summary – Bash Variables

Bash variables give scripts and sessions flexibility and dynamic behavior. From simple string assignments to exporting environment variables, mastering $var, export, and unset is crucial for scripting and system automation.

🔍 Key Takeaways:

• Variables are declared with var=value, accessed with $var
• export shares variables with subprocesses
• unset deletes any variable from the session
• Use quotes to handle spaces and avoid syntax errors

⚙️ Real-world Uses:

• Set paths (PATH, JAVA_HOME) dynamically
• Use variables in loops and conditions
• Pass configuration values into scripts

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❓ FAQ – Bash Variables

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❓ What does $var mean in Bash?
✅ $var is used to access the value of a variable. For example:

name="Linux"
echo $name  # Output: Linux

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❓ How do I export a variable for use in a script?
✅ Use:

export MY_VAR="somevalue"

Then the variable is accessible to any child shell or script.

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❓ How do I permanently set a variable in Bash?
✅ Add the variable to your ~/.bashrc or ~/.bash_profile and reload it:

source ~/.bashrc

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❓ What is the difference between unset and setting a variable to an empty string?
✅ unset varname removes the variable, while varname="" just clears its content but keeps it defined.

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❓ Can I use numbers in Bash variable names?
✅ Yes, but not at the beginning. Example:

user1="admin"   # ✅ valid
1user="admin"   # ❌ invalid

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