Variables and Command-Line Arguments in Bash

Variables allow your scripts to store and reuse values dynamically. Arguments let users pass custom inputs at runtime.

1. Defining and Using Variables

Assign variables without spaces around the = sign:

#!/bin/bash
# Define variables
APP_NAME="MyWebApp"
VERSION="1.0.3"

# Use variables by prefixing with $
echo "Deploying $APP_NAME version $VERSION"

2. Reading Command-Line Arguments

When you run a script with arguments, they are available via positional variables:

#!/bin/bash
# Usage: ./deploy.sh production v1.2.0

ENVIRONMENT=$1  # First argument
VERSION=$2      # Second argument

echo "Deploying to: $ENVIRONMENT"
echo "Version: $VERSION"

Special Argument Variables

3. Capturing Command Output

Assign the output of a command to a variable using $():

#!/bin/bash
# Capture current date and git commit hash
CURRENT_DATE=$(date +%Y-%m-%d)
LATEST_COMMIT=$(git rev-parse --short HEAD)

echo "Deploy timestamp: $CURRENT_DATE"
echo "Git commit: $LATEST_COMMIT"