Manipulation of config files with notepad is a burden for every developer / operator. It is the source of many errors.

With DEVOPS we try to automate this process. The result is less prone to errors. See the powershell script below to add a shared listener to a config file.

$configFile = "PATH_TO_YOUR.config"
$xml=New-Object XML
# Load the configuration from disk into memory
$xml.Load($configFile)
# Find the sharedListener named TextFileLogListener
$tracelistenernode = $xml.SelectSingleNode("/configuration/system.diagnostics/sharedListeners/add[@name='TextFileLogListener']")
if (!$tracelistenernode)
{
	# Create the filter element inside the listener
	$filter = $xml.CreateElement("filter")
	$filter.SetAttribute("type", "System.Diagnostics.EventTypeFilter")
	$filter.SetAttribute("initializeData", "Information")
	# Create the add element to add the shared listener
	$tracelistenernode = $xml.CreateElement("add")
	$tracelistenernode.SetAttribute("name", "TextFileLogListener")
	$tracelistenernode.SetAttribute("type", "System.Diagnostics.TextWriterTraceListener")
	$tracelistenernode.SetAttribute("initializeData", "c:\\log.txt")
	# Here is the filter added
	$tracelistenernode.AppendChild($filter)
	# You can use "fluent style" navigation
	$xml.configuration.'system.diagnostics'.sharedListeners.AppendChild($tracelistenernode)
	# Now create an entry in the trace listeners to the shared listener
	$listener = $xml.CreateElement("add")
	$listener.SetAttribute("name", "TextFileLogListener")
	$xml.configuration.'system.diagnostics'.trace.listeners.AppendChild($listener)
	# Save the config to disk
	$xml.Save($configFile)
}

You can run the script above and see the changes it makes to the config file. To prevent errors on multiple runs, the script checks the presence of TextFileLogListener and will only add it once.

This is part of our Automate test environment with Azure Virtual Machines script.