$time - time the log message was sent
$date - date the log message was sent
$message - the log message
$level - the log level
$node - the node that prints the message
$metadata - user controlled data presented in “key=val key2=val2” format
$levelpad - sets to a single space if level is 4 characters long, otherwise set to the empty space. Used to align the message after level.
In addition to the keys provided by the user via Logger.metadata/1, the following extra keys are available to the :metadata list:
:application - the current application
:module - the current module
:function - the current function
:file - the current file
:line - the current line
:pid - the current process ID