Bash Scripting Basics

What is the shebang line and how do you write a basic bash script?

Linuxbeginner

// interview question

What is the shebang line and how do you write a basic bash script?

Sample answer

The shebang (#!) tells the OS which interpreter to use. #!/bin/bash specifies bash. Basic script structure: shebang, variables (VAR=value), conditionals (if/then/fi), loops (for/while), and functions. Make scripts executable with chmod +x. Use set -e to exit on errors and set -x for debugging.

Why this matters

Bash scripting is essential for automating repetitive tasks, deployment scripts, system administration, and CI/CD pipelines. Even with modern tools like Ansible or Terraform, bash scripts remain valuable for quick automation and glue code.

Code examples

Basic script structure

bash

#!/bin/bash
set -e  # Exit on error

# Variables
APP_NAME="myapp"
ENV=${1:-"dev"}  # Default to 'dev' if no argument

# Function
deploy() {
  echo "Deploying $APP_NAME to $ENV..."
}

# Conditional
if [ "$ENV" = "prod" ]; then
  echo "Production deployment - extra caution!"
fi

deploy

Loops and input handling

bash

#!/bin/bash

# For loop
for server in web1 web2 web3; do
  echo "Checking $server..."
  ssh $server 'uptime'
done

# While loop reading file
while read -r line; do
  echo "Processing: $line"
done < servers.txt

# Check if command succeeded
if docker ps > /dev/null 2>&1; then
  echo "Docker is running"
else
  echo "Docker is not running"
  exit 1
fi

Common mistakes to avoid

Forgetting to quote variables (causes issues with spaces)
Using == instead of = in [ ] conditionals
Not handling script failures (use set -e or check $?)

Likely follow-ups

What's the difference between $* and $@ for script arguments?
How do you handle errors gracefully in bash scripts?
When would you choose bash over Python for automation?

Answer out loud first, then check yourself against the model answer.

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