Custom Format & Context
You can fully customize your logging output by adjusting the .format property of a destination. A simple but powerful variable-based syntax helps to achieve astonishing formatting, including JSON and color.
The character $ marks the start of "variable" followed by a case-sensitive letter.
Basic Example
let console = ConsoleDestination()
console.format = "$L: $M" // loglevel: message
log.addDestination(console)
log.debug("Hello World")
// log output:
DEBUG: Hello World
Setting the correct variables in .format gives you full customization.
For example, you can adjust the date format by setting it between $D and $d using the standard Swift datetime format syntax. You can also colorize content of supported destinations by wrapping it with $C and $c. The used color depends on the log level.
More Examples, Including JSON
// log hour, minute and second, filename, function, line, log level & message
console.format = "$DHH:mm:ss$d $N.$F():$l $L: $M"
// log output:
10:06:31 MyViewController.myFunction():123 DEBUG: a debug message
// log thread, date, time in milliseconds, level & message
console.format = "$Dyyyy-MM-dd HH:mm:ss.SSS$d $T $L: $M"
// log output:
2016-09-08 10:06:31.113 myThread DEBUG: My debug message
// log everything to a JSON string:
console.format = "$J"
// log output is JSON:
{"thread": "main", "file": "MyViewController.swift", "level": 1, "timestamp": 1487680870.503811, "message": "Hello World", "function": "myFunction()", "line": 123}
Format Variables
Each variable represents a particular data from the logging event and starts with a $:
| Variable | Description |
|---|---|
| $L | Level, for example "VERBOSE" |
| $M | Message, for example the foo in log.debug("foo") |
| $J | JSON-encoded logging object (can not be combined with other format variables!) |
| $N | Name of file without suffix |
| $n | Name of file with suffix |
| $F | Function |
| $l | Line (lower-case l) |
| $D | Datetime, followed by standard Swift datetime syntax |
| $d | Datetime format end |
| $T | Thread |
| $C | Color start, is just supported by certain destinations and is ignored if unsupported |
| $c | Color end |
| $U | Uptime in the format HH:MM:SS |
| $X | Optional context value of any type (see below) |
Default Format
If you do not adjust your format then the following pattern will be used (including color where possible):
.format = "$DHH:mm:ss.SSS$d $C$L$c $N.$F:$l - $M" // log output (DEBUG is in color): 2016-09-08 10:06:31.113 DEBUG MyViewController.myFunction():123 - My debug message
Context
Optionally you can add context data to each log message of any type. On output it is added to the end of the log message:
.format = "$L: $M $X" // show level, message and context value<br>// add context
log.debug("Message 1")
log.debug("Message 2", context: nil)
log.debug("Message 3", context: " yeah!")
log.debug("Message 4", context: 567)
log.debug("Message 5", context: [1, "a", 2])
// log output:
DEBUG: Message 1
DEBUG: Message 2
DEBUG: Message 3 yeah!
DEBUG: Message 4 567
DEBUG: Message 5 [1, \"a\", 2]