Bash — Variables

Assigning variables

#!/bin/bash

# No spaces around =!
name="Alice"
age=30
path="/home/user"

# Use variables
echo "Name: $name"
echo "Age: ${age}"

Read input

#!/bin/bash

read -p "Enter name: " name
read -sp "Enter password: " pass
echo
echo "Hello, $name"

Environment variables

#!/bin/bash

echo "Home: $HOME"
echo "User: $USER"
echo "Shell: $SHELL"
echo "Path: $PATH"

# Export to make available to child processes
export MY_VAR="hello"

Default values

#!/bin/bash

# Use default if unset
name="${1:-World}"
echo "Hello, $name!"

# Use default if unset or empty
name="${1:-World}"
echo "Hello, $name!"

Read-only variables

#!/bin/bash

readonly PI=3.14159
# PI=3.14  # Error: readonly variable

Array variables

#!/bin/bash

# Indexed array
fruits=("Apple" "Banana" "Cherry")
echo "${fruits[0]}"    # Apple
echo "${fruits[@]}"    # All elements
echo "${#fruits[@]}"   # Length: 3

# Associative array
declare -A ages
ages[Alice]=30
ages[Bob]=25
echo "${ages[Alice]}"

Variable scope

#!/bin/bash

global_var="I am global"

function test_scope() {
    local local_var="I am local"
    echo "$global_var"
    echo "$local_var"
}

test_scope
echo "$global_var"
# echo "$local_var"  # Error: not defined

Mini Practice

Write Bash code that:

1. Assigns and uses variables
2. Reads user input with read
3. Uses environment variables
4. Creates an indexed array

Up Next

In the next lesson, you'll learn about Strings — working with text in Bash.