If you’ve ever wished your computer could take over your repetitive tasks, like checking files, updating reports, or processing logs, then Bash for loops are about to become your new best friend.

We can say that Bash is the language that you can use to talk with your computer. And ever wondering, what is for loops? They’re like your loyal assistants who will repeat tasks as many times as you want, without getting tired.

But don’t worry if you’re not a programmer or a technical expert. We’re going to break everything down in simple terms so that anyone, even with zero scripting experience, can understand.

Ready to dive into automation and shell scripting? Let’s get started!

What is Bash and Why Use It?

Bash (short form of Bourne Again SHell) is a command-line interface used in Linux and macOS systems. You can use it to run commands, manipulate files, and automate tasks.

It’s like telling your computer what to do using text. And why should you care? Because Bash can save you hours of manual work with just a few lines of code.

What is a Loop in Programming?

Imagine you’re folding laundry. Each item goes through the same process, pick it up, fold it, and stack it. A loop in programming does the same thing: it repeats a set of actions until a condition is met.

Loops are essential for automation. They help you handle tasks like:

• Repeating commands
• Processing multiple files
• Running tests on different inputs

Introduction to Bash For Loops

For loops are most commonly used type of loop in Bash. They will repeat a task for the each item that included in a list.

For Example

for item in apple banana cherry
do
  echo $item
done

for item in apple banana cherry
do
  echo $item
done

The for loop in above example will print each fruit name on new line.

Output:

Basic Syntax of Bash For Loops

Here’s what the structure of a Bash for loop looks like:

for variable in list
do
  command(s)
done

for variable in list
do
  command(s)
done

• variable is a placeholder.
• list is a set of values.
• do starts the block of commands.
• done ends the block.

It’s that simple!

Example of Bash For Loop: Hello, World!

Let’s write a for loop that prints “Hello, World!” five times.

for i in {1..5}
do
  echo "Hello, World!"
done

for i in {1..5}
do
  echo "Hello, World!"
done

Output:

What’s happening here?

• “{1..5}” will run the loop from 1 to 5.
• “i” takes each value from 1 to 5.
• echo prints the message.

How Bash For Loops Work

Behind the scenes, Bash loops:

1. It will assign a value from list to loop variable to execute.
2. Execute the code block.
3. Repeat until all values are used.

Think of it as like passing buckets down a line, each person (the loop variable) gets a new bucket (value) and performs the same action.

Common Use Cases of Bash For Loops

You can use Bash for loops for tasks like:

• Renaming or moving files
• Automating backups
• Running scripts on multiple servers
• Reading lines from a file
• Monitoring system logs

Once you start using them, you’ll wonder how useful it is!

Bash For Loop with Numeric Ranges

Want to count from 1 to 10?

for i in {1..10}
do
  echo $i
done

for i in {1..10}
do
  echo $i
done

Output:

Or with step values:

for i in {1..10..2}
do
  echo $i
done

for i in {1..10..2}
do
  echo $i
done

In the output, it will print 1, 3, 5, 7, 9 as you can see in the image below.

Output:

Bash For Loop with Lists

You can manually define a list too:

for animal in cat dog cow
do
  echo "The animal is: $animal"
done

for animal in cat dog cow
do
  echo "The animal is: $animal"
done

Output:

Or use variables:

mylist="red blue green"
for color in $mylist
do
  echo $color
done

mylist="red blue green"
for color in $mylist
do
  echo $color
done

Output:

Nested For Loops

Want to loop inside another loop? That’s called nested loop.

for i in 1 2 3
do
  for j in A B
  do
    echo "$i$j"
  done
done

for i in 1 2 3
do
  for j in A B
  do
    echo "$i$j"
  done
done

This prints:
1A
1B
2A
2B
3A
3B

Output:

Control Statements in For Loops

You can control your loops with:

• break – exits the loop early
• continue – skips to the next iteration

Example:

for i in {1..5}
do
  if [ $i -eq 3 ]; then
    continue
  fi
  echo $i
done

for i in {1..5}
do
  if [ $i -eq 3 ]; then
    continue
  fi
  echo $i
done

This skips printing 3.

Output:

Tips for Writing Clean Bash For Loops

• Use meaningful variable names: file, user, line are better than i or x
• Comment your code so you remember what each part does
• Test your loops with small inputs before running them on large data sets

Common Mistakes and How to Avoid Them

Here are some beginner pitfalls:

• Forgetting do and done: Always include them
• Using wrong syntax: you can use {1..10}, but not 1-10
• Misusing spaces: Always leave spaces around in

Avoid these and your loops will run like a charm.

Conclusion 

Bash for loops are a simple yet powerful tool for anyone who wants to start automating tasks on their computer. Whether you’re a casual Linux user or a sysadmin, learning how to loop in Bash opens the door to endless possibilities. So go ahead, experiment, break things, and most importantly, automate like a pro!

Feeling overwhelmed by command-line tasks?
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Here’s what makes ServerAvatar a great companion:

• Easily handle server setups, app deployments, domains, databases, and more, no deep Linux knowledge required.
• Prefer working in the terminal? You’ll still have full SSH access and flexibility to script and automate as you like.

With ServerAvatar, whether you’re a beginner or a power user, you can manage servers your way, fast, secure, and hassle-free.

FAQs

3. How to loop files in a directory?

for file in *.txt
do
  echo "Found file: $file"
done

This will go through every .txt file in your current directory.