Home Beginner’s Guide to Bash While Loop with Easy Examples

Beginner’s Guide to Bash While Loop with Easy Examples

When you start learning Bash scripting, one of the most powerful tools you’ll come across is the bash while loop. It allows you to repeat tasks until a condition changes. Whether you want to count numbers, process a file, or keep a program running until you stop it, the while loop is the perfect choice.

In this article, we’ll break it down into simple terms with examples anyone can follow.

What is a Bash While Loop?

A bash while loop is a structure that keeps running a set of commands as long as a condition remains true. Once the condition becomes false, the loop stops.

The basic structure looks like this:

while [ condition ]
do
  # commands to run
done
  • condition → The check that decides if the loop continues
  • do → Marks the start of commands
  • done → Marks the end of commands

Simple Example of Bash While Loop

Let’s look at a simple script:

#!/bin/bash
i=1
while [ $i -le 5 ]
do
  echo "Number: $i"
  i=$((i+1))
done

Here’s what happens:

  • The first line #!/bin/bash is called a shebang. It tells the system to use Bash to run the script.
  • The variable i starts at 1
  • The condition [ $i -le 5 ] means “keep looping while i is less than or equal to 5”
  • Each round prints the value of i, then increases it by 1
  • When i becomes 6, the condition fails and the loop ends

Bash While Loop Example: Reading a File Line by Line

One of the most common uses of a bash while loop is reading files.

#!/bin/bash
filename="mydata.txt"
while IFS= read -r line
do
  echo "$line"
done < "$filename"

Explanation:

  • IFS= read -r line → Reads one line at a time safely into the variable line
  • done < "$filename" → Redirects the loop to take input from the file instead of the keyboard
  • The loop repeats until the entire file has been read

This method is reliable because it handles spaces and special characters correctly.

Infinite Bash While Loop

Sometimes you want a loop to run forever until you stop it manually. You can do this with a bash while loop:

#!/bin/bash
while :
do
  echo "Still running..."
  sleep 1
done
  • The : command always returns true
  • This makes the loop infinite
  • You can stop it anytime with Ctrl+C

This is handy for monitoring or background tasks.

Controlling the Loop with Break and Continue

Break – stop the loop early

#!/bin/bash
i=1
while :
do
  echo "i is $i"
  if [ $i -ge 5 ]
  then
    echo "Stopping loop"
    break
  fi
  (( i++ ))
done

Even though the loop is infinite, break forces it to end when i reaches 5.

Continue – skip one round

#!/bin/bash
i=0
while [ $i -lt 10 ]
do
  (( i++ ))
  if (( i % 2 != 0 ))
  then
    continue
  fi
  echo "Even number: $i"
done

In this case, the loop skips odd numbers and only prints even ones.

Why Use Bash While Loop?

The bash while loop is perfect when you don’t know how many times a task will repeat. Some benefits include:

  • Automating tasks until a condition changes
  • Reading data from files line by line
  • Running processes that wait for events
  • Flexible use of break and continue for control

Whether you’re a beginner or advanced user, learning while loops will save you time and effort in Bash scripting.

Final Thoughts

The bash while loop may look technical at first, but once you understand its structure, it becomes one of the easiest tools to automate repetitive tasks.

You now know:

  • How the basic structure works
  • How to use conditions like -le inside loops
  • What the shebang line does (#!/bin/bash)
  • How to read files and create infinite loops
  • How to control loops with break and continue

Mastering this will give you a solid foundation in Bash scripting and make your scripts more powerful and reliable.