How to Check If a File is Empty in Bash [6 Methods]

An empty file in Bash refers to a file with no content or a size of zero bytes. In Bash scripting, while working with files, it’s very important to learn how to check if a file is empty or not. To check if a file is empty, you can go for several methods such as using the -s option, wc command, -z option, grep command, stat command, and ls command.

In the following article, I’ll show you 6 methods to check if a file is empty in Bash:

1. Using “-s” Flag With “[ ]” Construct

The “-s” flag within an ‘if’ conditional statement is used to check the size of a file. In this effort,  the single square brackets [ ] can be used to perform the test operation. However, if the file within the test expression has a size greater than zero, it means the file contains some value and is not empty. But when using the NOT (!) operator with the -s flag, it inverts the output and returns a true expression if the file is empty.

Go through the following script to check if a file is empty in Bash:

#!/bin/bash

file_path="/home/nadiba/color.txt"
if [ ! -s "$file_path" ]; then
echo "The file 'color.txt' is empty."
fi

This image states that the file color.txt in my system is empty.

2. Using “wc” Command with “-c” Flag

The “wc (word count)” command with the “-c” flag within an if statement in Bash is used to count the number of bytes in a file. If the byte count is zero, it returns a true expression, meaning the file is empty. Otherwise, it returns nothing.

To learn how to check if a file is empty, use the wc -c command. Go through the following script:

#!/bin/bash

file_name=emoji.txt

#Checking if file has any lines
if [ $(wc -c < "${file_name}") -eq 0 ]; then
echo "'$file_name' is empty."
fi

This image states that the file emoji.txt I have checked in my system is empty.

3. Using “-z” Flag

The “-z” option in Bash mainly checks if a string is empty. Using this -z option along the cat command is an effective way to check for an empty file (completely empty) i.e. the file that contains no lines or includes only whitespaces.

If you want to check for an empty file, use the -z option. Here is how:

#!/bin/bash

file_name=emoji.txt

if [ -z "$(cat ${file_name})" ]; then
echo "The file is empty."
fi

In the image, you can see that the file emoji.txt in my system is empty.

4. Using “grep” Command with “-q” Flag

The grep command in Bash is generally used for pattern matching. However, it can be used with the -q flag to indirectly check if a file is empty or has any content.

Review the script below to check if a file is empty in Bash:

#!/bin/bash

file_name=example.txt

if ! grep -q . "${file_name}"; then
echo "'example.txt' is empty."
fi

From the image, you can see that the file example.txt in my system is empty.

5. Using “stat” Command with “-c” Flag

The stat command is a utility in Bash that is used to retrieve information about files and filesystems. This command can be conjugated with the “-c” flag to display the size of the file in bytes. If a file size is zero bytes, the file is empty. Otherwise, it means that the file is not empty.

To check if a file is empty in Bash, use the stat -c command:

#!/bin/bash

filename=function.sh

if [ $(stat -c %s "${filename}") -eq 0 ]; then
echo "The file '$filename' is empty."
fi

This image dictates that the file function.sh in my system is empty.

6. Using “ls” Command

The ls command with the “-l” flag (long listing format) in Bash is used to display detailed information about files such as ownership, file size, permissions etc. This command can indirectly check if a file is empty in Bash by evaluating the size of that file. If the file has a size of zero bytes, it is considered an empty file.

Here’s how you can check if a file is empty in Bash using the ls -l command:

#!/bin/bash

file_name="abstract.txt"

#Getting the size of the file using ls -l and extracting the file size column
file_size=$(ls -l "$file_name" | awk '{print $5}')

#Checking if the file size is equal to zero
if [ "$file_size" -eq 0 ]; then
echo "The file '$file_name' is empty."
fi

From the image, you can see that the file abstract.txt in my system is empty.

Conclusion

As you can see, there are many ways to check if a file is empty in Bash, choose an appropriate one that suits your requirements. But before checking the emptiness of a file, make sure that it exists in your system.

People Also Ask

Can I perform a file emptiness check within a one-liner in Bash?

Yes, you can perform a file emptiness check within a one-liner in Bash by using the ‘-s’ flag with the [ ] construct. For example:

#!/bin/bash

if [ ! -s "file.txt" ]; then echo "The file is empty"; fi

Can I distinguish between an empty file and a non-existent file in Bash?

Yes, you can distinguish between an empty file and a non-existent file in Bash by performing different ‘if’ conditional tests using the syntaxes [ -s "FILENAME" ] and [ -e "FILENAME" ]. For Example:

#!/bin/bash

#Checking if the file exists
if [ -e "filename.txt" ]; then

#Checking if the file is empty
if [ -s "filename.txt" ]; then
echo "The file exists and is not empty."
else
echo "The file exists but is empty."
fi
else
echo The file does not exist."
fi

How can I handle cases where a file appears empty but contains whitespace or special characters?

To handle cases where a file appears empty but contains whitespaces (tabs, spaces or newlines) or special characters, you should consider the content of a file as well as the file size. Here’s how you can do so:

Checking for non-whitespace characters using the grep command:

#!/bin/bash

if grep -q '[^[:space:]]' "filename.txt"; then
echo "The file contains non-whitespace characters."
else
echo "The file is either empty or contains only whitespaces."
fi

Checking for files containing non-whitespace characters by trimming whitespaces and checking length:

#!/bin/bash

trimmed_file_content=$(< "filename.txt" tr -d '[:space:]')

if [ -n "$trimmed_file_content" ]; then
echo "The file contains non-whitespace characters."
else
echo "The file is either empty or contains only whitespaces."
fi

Are there implications for empty file detection in cross-platform Bash scripting?

Yes, cross-platform Bash scripting can have implications with empty file detection because of differences in behaviors, commands, and file system rules in different environments.

Can an empty file have metadata or attributes that distinguish it from non-empty files?

Yes, an empty file can have metadata or attributes that distinguish it from non-empty files. The file attributes that can distinguish empty files from non-empty ones are file size, and timestamps (creation time, modification time, and access time).

What’s the distinction between a file with zero bytes and an empty file containing whitespace characters?

A file with zero bytes is empty and contains no characters (including whitespaces). On the other hand, an empty file containing whitespace characters is not a zero-byte file and contains hidden characters.

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