Test if file or directory exists

https://www.tldp.org/LDP/abs/html/fto.html

Check if regular file exists:

if [ -f "/path/to/file" ]
then
  echo "Exists";
fi

Check if not regular file (or does not exist):

if [ ! -f "/path/to/file" ]
then
  echo "Not file";
fi

Check if file is a directory:

if [ -d "/path/to/dir" ]
then
  echo "Exists";
fi

Check if file is not a directory (or does not exist):

if [ ! -d "/path/to/dir" ]
then
  echo "Not directory";
fi