How do you check if a file is empty in shell scripting?

You can check if a file is empty in Shell scripts using various methods. Here are two commonly used methods:

Method 1: Using the -s File Test Operator

In Shell, the -s operator checks if a file is not empty. It returns true if the file exists and has a size greater than zero. Conversely, it returns false if the file is empty or does not exist.

bash
filename="example.txt"

if [ -s "$filename" ]; then
    echo "File '$filename' is not empty."
else
    echo "File '$filename' is empty or does not exist."
fi

This method is straightforward and quickly helps determine if a file is empty.

Method 2: Using the wc -l Command

Another approach is to use the wc -l command, which counts the number of lines in a file. If the file is empty, the line count will be zero.

bash
filename="example.txt"

line_count=$(cat "$filename" | wc -l)

if [ "$line_count" -eq 0 ]; then
    echo "File '$filename' is empty."
else
    echo "File '$filename' is not empty, with $line_count lines."
fi

This method is somewhat more complex as it determines file emptiness by counting lines. It not only detects if a file is empty but also provides the specific line count for non-empty files, offering richer information.

Summary

Both methods effectively check if a file is empty in Shell scripts. The choice depends on specific requirements and circumstances. If you only need to simply determine if a file is empty, using the -s operator may be simpler. If you need more detailed information about the file content (such as line count), consider using the wc -l command.