Last updated: 2006-09-18

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Conditions

Conditions are used in various places to filter log events based on their content.

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

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 .SQL or .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

The following functions are available:

Name	Description	Defined in
contains(s1,s2)	Determines whether the second string is a substring of the first one. Returns: true when the second string is a substring of the first string, false otherwise.	NLog.dll
ends-with(s1,s2)	Determines whether the second string is a suffix of the first one. Returns: true when the second string is a prefix of the first string, false otherwise.	NLog.dll
equals(o1,o2)	Compares two objects for equality. Returns: true when two objects are equal, false otherwise.	NLog.dll
length(s)	Returns the length of a string. Returns: The length of a string.	NLog.dll
starts-with(s1,s2)	Determines whether the second string is a prefix of the first one. Returns: true when the second string is a prefix of the first string, false otherwise.	NLog.dll