Shell Scripting Fundamentals

Question

What are the essential components of a shell script? Explain variables, conditionals, and loops.

Answer

Shell scripts automate command sequences. Essential components: 1) Shebang (#!/bin/bash) - specifies interpreter. 2) Variables - store values, accessed with $. 3) Conditionals (if/elif/else) - control flow based on conditions. 4) Loops (for, while) - iterate over items or until condition. 5) Functions - reusable code blocks. 6) Exit codes - indicate success (0) or failure (non-zero). Always quote variables and use 'set -e' for error handling.

Why This Matters

Shell scripting is the glue of DevOps - automating repetitive tasks, deployment scripts, cron jobs, and system administration. Bash is most common on Linux, but principles apply to other shells. Well-written scripts include error handling, logging, and are idempotent when possible.

Code Examples

Basic script structure

bash

Functions and error handling

bash

Common Mistakes

Not quoting variables, causing word splitting issues
Forgetting to handle error cases (missing 'set -e')
Using 'rm -rf $VAR' without checking if VAR is set

Follow-up Questions

Interviewers often ask these as follow-up questions

What does 'set -euo pipefail' do and why is it important?
How do you pass arguments to a shell script?
What is the difference between single and double quotes in bash?