for loop (list-based) in Bash Scripting

Introduction

A for loop helps you repeat actions for each item in a list. It saves time and avoids writing the same code many times.

You want to print each file name in a folder.

You need to run a command on several servers one by one.

You want to process a list of user names to create accounts.

You want to check each word in a list for spelling.

You want to automate tasks that repeat for many items.

Syntax

Bash Scripting

for item in list
 do
   commands using "$item"
 done

The list can be words, file names, or any items separated by spaces.

Use double quotes around "$item" to handle items with spaces.

Examples

Prints each color name from the list.

Bash Scripting

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

Prints all files ending with .txt in the current folder.

Bash Scripting

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

Handles names with spaces by quoting each item.

Bash Scripting

for name in "Alice" "Bob Smith" "Charlie"
 do
   echo "Hello, $name!"
 done

Sample Program

This script loops over a list of fruits and prints a message for each one.

Bash Scripting

#!/bin/bash

# List of fruits
fruits="apple banana cherry"

echo "Fruits before loop: $fruits"

for fruit in "$fruits"
 do
   echo "I like $fruit"
 done

Important Notes

Time complexity is O(n), where n is the number of items in the list.

Space complexity is low, just storing the list and current item.

Common mistake: forgetting to quote "$item" can cause errors if items have spaces.

Use for loops when you have a fixed list of items. Use while loops for conditions or unknown counts.

Summary

A for loop repeats commands for each item in a list.

Always quote variables like "$item" to handle spaces safely.

For loops are simple and great for running commands on many items.