View Source Logger.Backends.Console (Logger v1.13.4)
A logger backend that logs messages by printing them to the console.
Options
:level
- the level to be logged by this backend. Note that messages are filtered by the general:level
configuration for the:logger
application first.:format
- the format message used to print logs. Defaults to:"\n$time $metadata[$level] $levelpad$message\n"
. It may also be a{module, function}
tuple that is invoked with the log level, the message, the current timestamp and the metadata.:metadata
- the metadata to be printed by$metadata
. Defaults to an empty list (no metadata). Setting:metadata
to:all
prints all metadata. See the "Metadata" section for more information.:colors
- a keyword list of coloring options.:device
- the device to log error messages to. Defaults to:user
but can be changed to something else such as:standard_error
.:max_buffer
- maximum events to buffer while waiting for a confirmation from the IO device (default: 32). Once the buffer is full, the backend will block until a confirmation is received.
The supported keys in the :colors
keyword list are:
:enabled
- boolean value that allows for switching the coloring on and off. Defaults to:IO.ANSI.enabled?/0
:debug
- color for debug messages. Defaults to::cyan
:info
- color for info and notice messages. Defaults to::normal
:warn
- color for warning messages. Defaults to::yellow
:error
- color for error and higher messages. Defaults to::red
See the IO.ANSI
module for a list of colors and attributes.
Here is an example of how to configure the :console
backend in a
config/config.exs
file:
config :logger, :console,
format: "\n$time $metadata[$level] $levelpad$message\n",
metadata: [:user_id]
Custom formatting
The console backend allows you to customize the format of your
log messages with the :format
option.
You may set :format
to either a string or a {module, function}
tuple if you wish to provide your own format function. Here is an
example of how to configure the :console
backend in a
config/config.exs
file:
config :logger, :console,
format: {MyConsoleLogger, :format}
And here is an example of how you can define MyConsoleLogger.format/4
from the above configuration:
defmodule MyConsoleLogger do
def format(level, message, timestamp, metadata) do
# Custom formatting logic...
end
end
It is extremely important that the formatting function does
not fail, as it will bring that particular logger instance down,
causing your system to temporarily lose messages. If necessary,
wrap the function in a rescue
and log a default message instead:
defmodule MyConsoleLogger do
def format(level, message, timestamp, metadata) do
# Custom formatting logic...
rescue
_ -> "could not format: #{inspect({level, message, metadata})}"
end
end
The {module, function}
will be invoked with four arguments:
- the log level: an atom
- the message: this is usually chardata, but in some cases it may contain invalid data. Since the formatting function should never fail, you need to prepare for the message being anything
- the current timestamp: a term of type
Logger.Formatter.time/0
- the metadata: a keyword list
You can read more about formatting in Logger.Formatter
, especially
if you want to support custom formatting in a custom backend.