How to Loop Over Files in Directory in Bash

1. Loop Through Files
2. Loop Over Directory
3. Write All Files Inside the Directory Using Loop
4. Make Backups of All Files Inside the Directory

Loops in Bash have made it feasible to do operations on many files. You must have some privileges to work with files and folders.

The most effective method is looping, which allows the user to apply the same logic to the object again by utilizing a simple code line.

Loop Through Files

First, we will create a test directory and create multiple files inside the directory. Let’s create five files in test directory as file1.txt, file2.txt, file3.txt, file4.txt, and file5.txt.

We created a test folder using mkdir and created five files inside it using the touch command.

Loop Over Directory

Let’s loop over the newly created test directory and display the file names inside the directory. We’ll use for loop to do this.

~/test$ for file in *; do echo $file; done

Navigate to the test directory and enter the above command after $. * denotes all files inside the directory.

Output:

file1.txt
file2.txt
file3.txt
file4.txt
file5.txt

Write All Files Inside the Directory Using Loop

To write Hello World! in each file, we’ll use the for loop to iterate over files and the -e flag in echo to preserve newlines.

~/test$ for file in *; do echo -e "$file\nHello World!"> $file ; done

$file will show the file name at the beginning of the file, and \n will break the line, and Hello World! will be previewed in the second line. To check the data we added to the file, we need to display it using cat with a for loop.

~/test$ for file in *; do cat $file ; done

Output:

file1.txt
Hello World!
file2.txt
Hello World!
file3.txt
Hello World!
file4.txt
Hello World!
file5.txt
Hello World!

Make Backups of All Files Inside the Directory

.bak extension denotes the backup files. We’ll use cp with for loop to create backups.

~/test$ for file in *; do cp $file "$file.bak" ; done

You can use ls -l to list all the files inside the test directory.

~/test$ ls -l

Let’s check out the test directory.

You can see that backup files were created with suffixed .bak extension inside the folder.