In Bash, you can check if a file exists using the test command or the equivalent [ command. The most common way to check if a file does not exist is by using the -e option, which tests whether a file exists. To check if a file does not exist, you can negate this option using !, like this:

if [ ! -e /path/to/file ]; then

    echo "File does not exist"

fi


Alternatively, you can use the -f option to check if a file exists and is a regular file:
if [ ! -f /path/to/file ]; then

    echo "File does not exist or is not a regular file"

fi


You can also use the [[ ... ]] construct instead of the [ ... ] command. Here's an example:
if [[ ! -e /path/to/file ]]; then

    echo "File does not exist"

fi


Note that the file path can be absolute or relative. If it's a relative path, it's relative to the current working directory.