Introduction

Tired of typing the same commands over and over? In this post we’ll expand on the short video that showed how to build a simple Bash script using variables, loops, and conditionals. By the end you’ll understand the core Bash constructs and be ready to automate your daily Linux tasks.

Why Script?

Repeating commands manually wastes time and introduces human error. A script captures the logic once, makes it portable, and can be version‑controlled.

Core Concepts

Variables

In Bash a variable is defined without spaces:

greeting="Hello"

You reference it with a leading $:

echo "$greeting, world"

Quotes preserve whitespace and prevent word splitting.

Loops

The for loop can iterate over a range:

for i in {1..5}; do
  echo "Iteration $i"
done

The {1..N} brace expansion generates the sequence automatically.

Conditionals

Bash offers several test syntaxes. For arithmetic you can use (( )):

count=3
if (( count > 2 )); then
  echo "Count is high"
else
  echo "Count is low"
fi

A compact ternary‑style expression can be written with && and ||:

(( i % 2 )) && echo "odd $i" || echo "even $i"

Full Example: Greeting with Odd/Even Logic

Create a file called automate.sh:

#!/bin/bash
greeting="Hello"
for i in {1..3}; do
  (( i % 2 )) && echo "$greeting, odd $i" || echo "$greeting, even $i"
done

Make it executable and run it:

chmod +x automate.sh
./automate.sh

Output:

Hello, odd 1
Hello, even 2
Hello, odd 3

Best Practices

• Shebang: Always start scripts with #!/usr/bin/env bash or #!/bin/bash to guarantee the interpreter.

• Quote Variables: Use double quotes around variables ("$var") to avoid word splitting and globbing.

• Set -e and -u: Add set -euo pipefail at the top of scripts to exit on errors, treat unset variables as errors, and catch pipeline failures.

• Use Functions: Break complex logic into reusable functions.

• Avoid eval: It can lead to security vulnerabilities.

• Prefer $(...) over backticks: For command substitution, $(command) is more readable and nestable.

Common Pitfalls

Extending the Script

You can turn the example into a generic utility:

#!/usr/bin/env bash
set -euo pipefail

greeting="${1:-Hello}"
max="${2:-5}"

for i in $(seq 1 "$max"); do
  if (( i % 2 )); then
    echo "$greeting, odd $i"
  else
    echo "$greeting, even $i"
  fi
done

Now you can call it with custom greeting and count:

./automate.sh "Hi there" 7

Conclusion

Encapsulating repetitive logic in Bash scripts saves time, reduces errors, and makes your workflow reproducible. Start small, apply the best practices above, and gradually build more sophisticated automation pipelines.