How can you use shell to determine if a file exists?

You can use the following command to check if a file exists:

if [ -f /path/to/file ]; then
    echo "File exists"
else
    echo "File does not exist"
fi

The -f option here is used to check if a file exists and is a regular file. If the file exists, it will output “File exists”, otherwise it will output “File does not exist”. You can modify the path and output information as needed.