Conditions
Conditions are used in various places to filter log events based on their content.
Condition language
NLog supports a simple language to express conditions. The language consists of:
- relational operators (==, !=, <=, <=, >= and >)
- and, or, not boolean operators
- string literals which are always evaluated as layouts - '${somerenderer}'
- boolean literals - true and false
- log level literals - LogLevel.Trace, LogLevel.Debug, ... LogLevel.Fatal
- numeric literals - 12345 (integer literal) and 12345.678 (floating point literal)
- predefined keywords to access the most common log event properties - level, message and logger
- braces - to override default priorities and group expressions together
Examples
Here are some examples of conditions:
- level > LogLevel.Debug - matches the messages whose level is greater than Debug
- (level > LogLevel.Debug) or contains(message,'xxx') - matches the messages whose level is greater than Debug or which include the xxx substring in the log message
- starts-with(logger,'Kopytko.') - matches the loggers whose names start with
Kopytko. - ends-with(logger,'.SQL') or ends-with(logger,'.XML') - matches the loggers whose names end with either
.SQLor.XML - true - matches everything
- false - matches nothing
- length(message) > 100 - matches the log events where the length of the log message is greater than 100
- '${shortdate}' == '2005-11-10' - matches on the specified date
Available functions
The following functions are available:
| Name | Description | |
|---|---|---|
| contains(s1,s2) | Determines whether the second string is a substring of the first one.
Returns: | NLog.dll |
| ends-with(s1,s2) | Determines whether the second string is a suffix of the first one.
Returns: | NLog.dll |
| equals(o1,o2) | Compares two objects for equality.
Returns: | NLog.dll |
| length(s) | Returns the length of a string.
Returns: | NLog.dll |
| starts-with(s1,s2) | Determines whether the second string is a prefix of the first one.
Returns: | NLog.dll |
