How to check if a file is empty in Bash?

Checking if a file is empty in Bash can be achieved in multiple ways. I will introduce two commonly used methods:

Method 1: Using the -s File Test Operator

In Bash, the -s operator checks if a file is not empty. It returns true if the file exists and its size is greater than zero; otherwise, it returns false. You can use the logical negation operator ! to check if the file is empty.

bash
if [ ! -s /path/to/your/file ]; then
  echo "File is empty"
else
  echo "File is not empty"
fi

This method is straightforward, as it verifies whether the file size exceeds zero to determine if the file is empty.

Method 2: Using the stat and wc Commands

Another approach involves using the stat command to retrieve the file size and the wc command to count the bytes. If the byte count is zero, the file is empty.

bash
filesize=$(stat -c %s /path/to/your/file)
if [ "$filesize" -eq 0 ]; then
  echo "File is empty"
else
  echo "File is not empty"
fi

This method accurately obtains the file size via stat and employs conditional statements for size comparison.

Practical Application Example

Suppose you are developing a script that checks if a log file is empty to decide whether to send an email notification to the administrator.

bash
logfile="/var/log/myapp.log"

if [ ! -s "$logfile" ]; then
  echo "Log file is empty; no email needed."
else
  echo "Log file is not empty; sending email..."
  # Assume code to send email is present here
fi

Such scripts effectively assist system administrators in automating routine tasks and enhancing efficiency.

In summary, checking if a file is empty is a common requirement, and Bash offers multiple concise methods to achieve this. Select the most appropriate method based on your specific application scenario.