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Var Layout Renderer
Render a NLog variable. The variable value can be set from the XML config and/or the API.
Platforms Supported: All
Introduced in 4.1, see also news post
⚠️ NLog Config Variables are very similar to global variables. They should stay immutable and not be updated for every logevent. There are better ways to include local context for a single LogEvent.
Performance is better when using NLog variables directly in config file (Ex.
${myvar}), instead of using this layout renderer that always performs dynamic lookup (Ex.${var:myvar}). But this layout renderer reacts to NLog variables being modified at runtime.
Modifying NLog variables at runtime together with NLog configuration changes/reload can cause unexpected changes to NLog variables and produce unexpected output. Consider using GDC layout renderer for simple values, that doesn't make use of NLog Layout logic.
${var:name=String:default=String}
- name - Name of the NLog variable. Required.
-
default - Default value to be used when the variable is not set.
Not used if name is
null
<nlog>
<variable name="user" value="admin" />
<variable name="password" value="realgoodpassword" />
<targets>
<target name="debug" type="Debug" layout="${message} and ${var:user}=${var:password}" />
</targets>
<rules>
<logger name="*" minlevel="Debug" writeTo="debug" />
</rules>
</nlog>// create or edit
LogManager.Configuration.Variables["user"] = "admin";
LogManager.Configuration.Variables["password"] = "123";
// or remove
LogManager.Configuration.Variables.Remove("password");- Variables can be changed, deleted and created from the API
- A default value can be configured for a variable, e.g.
${var:password:default=unknown} - The old variables can still be used and so this is completely backwards-compatible.
- the
<variable>is optional if no default is needed - Variables configured at runtime will be reset on
autoReload="true", unless also usingkeepVariablesOnReload="true"(Before NLog 5.0 thenkeepVariablesOnReloadwas default false) - Variables configured at runtime will be reset when new NLog LoggingConfiguration is assigned (This is not the case for GDC layout renderer)
- Troubleshooting Guide - See available NLog Targets and Layouts: https://nlog-project.org/config
- Getting started
- How to use structured logging
- Troubleshooting
- FAQ
- Articles about NLog
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All targets, layouts and layout renderers
Popular: - Using NLog with NLog.config
- Using NLog with appsettings.json