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Often you'll need to check if a file is empty, and luckily there are some easy ways to do this using Bash in the terminal or even using a Bash script.

Use the test command with the -s option flag in Bash to check if a file is empty

The test command is one of the most useful shell built-in commands and has many options for files and directories. The -s option of the test command checks if the size of a file is greater than 0.

If the file size is greater than zero, the command will return true. Otherwise, it will return false.

The following demonstrates test -sthe use of . We will use examples to explain the test command.

In this example, we have a file called newFile.txt. We will create a Bash script called empty_test.sh as follows:

#!/bin/bash
test -s newFile.txt && echo "file has something" || echo "file is empty"

If the file newFile.txt is empty, the shell will have the following output:

On the other hand, if newFile.txt has any content, for example:

Hello!

The output will then look like this:

The above command is a straightforward way to check if the selected file is empty. If test -s newFile.txtevaluates to true, it will print file has something.

Otherwise, it prints file is empty. This command can be used in a Bash script or run directly in a terminal.

It is important to note that if the command is used in a different directory or level than the file being checked, the full file path needs to be written.

There is an alternative way to write the above command. In Bash, [ is also a shell builtin and is equivalent to the test command:

#!/bin/bash
[ -s newFile.txt ] && echo "file has something" || echo "file is empty"

This command is equivalent to the one we used previously.

We can also use test -sthe command to find all empty files in a given directory:

#!/bin/bash
for file in *.txt;
do if [ ! -s $file ];
then echo $file;
fi;
done

The above command will print the names of all empty .txt files in the directory. You can easily customize it to check for different types of files by simply replacing .txt with another extension.

Check if a file is empty using ls command in Bash

The ls command lists all the files and subdirectories in the current directory. The ls command can also be used with the -s option flag to display the size of the file next to the file name.

For example, if we run the command in a test directory we created that contains two subdirectories and a .docx file ls -s, we will get the following output:

It is important to note that in macOS, this command will display the size of all subdirectories as 0. This is regardless of whether the subdirectories contain other content.

Also note that the default shell used is zsh (not bash). However, this is not a difference caused by the shell but by the operating system itself.

To illustrate this result in a Linux environment, specifically using bash, we created a test folder that contains two empty directories named Test 1 and Test 2. It also contains two text files, test.txt has a small string in it and test2.txt is a blank text file.

Subdirectories are displayed as 4 KB regardless of the size of the contents. This does not represent the actual contents of the folder; it is the space taken up by the entries themselves.

A better approach is to use the ls command with the -l option flag, as this will display more information in a tabular format:

ls -l

We will run this command in the same test directory as before. The output will be as follows:

As shown above, ls -lthe command provides more information and displays the correct size of the subdirectories.

To view sizes in KB, MB, and GB, use the -h option -lh. Include the -h flag to make the data easier to read.

The output will be similar to the following: