Simple fish shell command to give a daycount between YYYY-MM-DD and now.

daycount.fish

# Print the number of days between a given date or the default date and the current date.
#
function daycount
  # Default date.
  set DATE "2020-02-17"
  
  # Test for presence and formatting of argument.
  if count $argv > /dev/null
    if string match -qr '^([12]\d{3}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01]))$' $argv
      set DATE $argv
    else
      echo "Date must be in YYYY-MM-DD format."
      return 1
    end
  end
  
  set ELAPSED (php -r "echo date_diff(date_create('$DATE', new DateTimeZone('America/New_York')),date_create('now', new DateTimeZone('America/New_York')))->format('%a');")
  echo "Elapsed: $ELAPSED days"
end