Environment variables vs local variables in Bash Scripting

Introduction

Environment variables store information for the system and other programs, while local variables store data only inside a script or shell session.

When you want to share a setting or path with multiple programs, use environment variables.

When you need a temporary value only inside your script, use local variables.

When you want to keep data private to your script and not affect other programs, use local variables.

When you want to configure your shell or programs globally, use environment variables.

When testing or debugging a script, use local variables to avoid changing system settings.

Syntax

Bash Scripting

local local_variable=value
export ENV_VARIABLE=value

Local variables are created by assigning a value without 'export'.

Environment variables are created by using 'export' before the variable.

Examples

Creates a local variable 'name' and prints it.

Bash Scripting

name="Alice"
echo $name

Adds a folder to the environment variable PATH and prints it.

Bash Scripting

export PATH="/usr/local/bin:$PATH"
echo $PATH

Shows both local and environment variables in the same script.

Bash Scripting

local_var="hello"
export ENV_VAR="world"
echo $local_var
echo $ENV_VAR

Sample Program

This script shows the difference: local_var is only inside this script, ENV_VAR is passed to the new shell.

Bash Scripting

#!/bin/bash

# Local variable
local_var="I am local"

# Environment variable
export ENV_VAR="I am environment"

# Print both
 echo "Local variable: $local_var"
 echo "Environment variable: $ENV_VAR"

# Start a new shell to check if variables exist there
bash -c 'echo "Inside new shell - Local: $local_var"; echo "Inside new shell - Env: $ENV_VAR"'

Important Notes

Local variables disappear when the script or shell ends.

Environment variables are inherited by child processes but not by parent or sibling processes.

Use 'export' carefully to avoid accidentally changing system-wide settings.

Summary

Local variables exist only inside the current script or shell session.

Environment variables are shared with child processes and other programs.

Use 'export' to make a variable an environment variable.