until loop in Bash Scripting

Introduction

An until loop repeats commands until a condition becomes true. It helps run tasks while waiting for something to happen.

When you want to keep trying a command until it succeeds.

When you want to wait for a file to appear before continuing.

When you want to repeat a task until a certain number is reached.

When you want to check a condition and run commands until it changes.

Syntax

Bash Scripting

until [ condition ]
do
  commands
 done

The loop runs while the condition is false.

Once the condition becomes true, the loop stops.

Examples

This loop prints the count from 1 to 3.

Bash Scripting

count=1
until [ $count -gt 3 ]
do
  echo "Count is $count"
  count=$((count + 1))
done

This loop waits until the ping command succeeds.

Bash Scripting

until ping -c 1 example.com
 do
  echo "Waiting for network..."
  sleep 2
done

Sample Program

This script prints numbers from 1 to 5 using an until loop.

Bash Scripting

#!/bin/bash

count=1
until [ $count -gt 5 ]
do
  echo "Number: $count"
  count=$((count + 1))
done

Important Notes

Make sure the condition will eventually become true to avoid infinite loops.

Use clear and simple conditions for easier understanding.

You can use break inside the loop to stop it early if needed.

Summary

An until loop runs commands until a condition is true.

It is useful for repeating tasks while waiting for something.

The loop stops as soon as the condition becomes true.