For Loop in Bash

A for loop in Bash is a control structure that allows you to repeat a set of commands for each item in a list, over a range, or based on other criteria. It’s commonly used for tasks like iterating over files in a directory, processing elements in an array, or executing a block of code multiple times.

Basic Syntax

The basic syntax of a for loop in Bash is as follows:

for VARIABLE in LIST
do
    # Commands to be executed
done

• VARIABLE is a placeholder that takes the value of each item in LIST one by one.
• LIST can be a list of values, a range of numbers, or even a command that generates a list.
• The do and done keywords define the start and end of the loop block.

  Example 1: Loop Over a List of Values

  Here’s an example of a for loop that iterates over a list of words:

  for word in apple banana cherry
  do
      echo "The fruit is: $word"
  done

Output:

The fruit is: apple
The fruit is: banana
The fruit is: cherry

Example 2: Loop Over a Range of Numbers

You can also loop over a sequence of numbers:

for i in {1..5}
do
    echo "Number: $i"
done

Output:

Number: 1
Number: 2
Number: 3
Number: 4
Number: 5

Example 3: Loop Over Files in a Directory

A common use case is looping over files in a directory:

for file in /path/to/directory/*
do
    echo "Processing $file"
done

This loop will iterate over each file in the specified directory and execute the commands inside the loop for each file.
For example, read all files from /home/john directory.

for file in /home/john/*
do
    echo "Processing $file"
done

Output:

Processing /home/john/Desktop
Processing /home/john/Documents
Processing /home/john/Downloads
Processing /home/john/Music
Processing /home/john/Pictures
Processing /home/john/Public
Processing /home/john/Templates
Processing /home/john/Videos
Processing /home/john/snap
Processing /home/john/tut

Example 4: C-Style For Loop

Bash also supports a C-style for loop, similar to loops in languages like C or Java:

for (( i=1; i<=5; i++ ))
do
    echo "Iteration $i"
done

Output:

Iteration 1
Iteration 2
Iteration 3
Iteration 4
Iteration 5

Summary

• for loops are versatile and can be used to iterate over lists, ranges, or output from commands.
• They are useful for automating repetitive tasks, processing files, and more.

This should give you a solid understanding of how to use for loops in Bash scripts.