File appender
The file appender can be used to write log messages to a file. It uses Lua I/O routines to do its job.
function logging.file(filename, [datePattern], [logPattern])
- filename:
 The name of the file to be written to. On each call to log a message the file is opened for appending and closed immediately.
 If the file cannot be opened for appending the logging request returns nil and an error message.
- datePattern:
 This is an optional parameter that can be used to specify a date pattern that will be passed to the- os.datefunction to compose the filename.
 This is useful to create daily or monthly log files. If the user wants to create one log file per day he specifies a- "%Y-%m-%d"pattern and a filename like- "temp%s.log".
- logPattern:
 A pattern can be specified to control how the message is written.
 The default value is- "%date %level %message\n".
Example
require"logging.file"
local logger = logging.file("test%s.log", "%Y-%m-%d")
logger:info("logging.file test")
logger:debug("debugging...")
logger:error("error!")
