When automating tasks, such as software installation, using Powershell, it is useful to output to a logfile for fault finding purposes, but I have never liked the idea of creating log files, as these are not easily managed and can build up over time. Another problem is that no-one, other than yourself, is likely to know that the logs exist, or where it is located. Everyone, however, knows about the Windows Eventlog and how to access it, so it makes sense to log your information there.
Adding script output to the Windows Eventlog is reasonably straightforward, but has to be done in the correct way. To use the Eventlog you need to create two items, a new Eventlog and a Source for the log entries. Optionally you can then configure the log that you have created. The code for this is below.
New-EventLog -LogName Application -Source "Documentum_Webtop-AddIn_1.0_x86_R01" Limit-EventLog -OverflowAction OverWriteAsNeeded -MaximumSize 64KB -LogName Application
The first line of code creates a log called Application, with a source called Documentum_Webtop-AddIn_1.0_x86_R01. The source is simply the packaged application that I am going to be installing. Using this name makes it easy to identify log entries from the application within the Eventlog.
The second line of code sets the maximum size of the log to 64Kb and configures the log to overwrite when it gets to the maximum size.
I can now write to the Eventlog by using the following command.
Write-EventLog -LogName "Application" -Source "Documentum_Webtop-AddIn_1.0_x86_R01" -EventID 25001 -EntryType Information -Message "Begining install of Application Documentum_Webtop-AddIn_1.0_x86_R01"
The EventID should be 25000 or greater, as this range is undocumented.
ErrorType can be Information, Warning or Error.
When writing install and uninstall scripts, I like to include the New-Eventlog and Limit-EventLog entries at the beginning of the Install script, and then remove the Source at the end of the Uninstall script. This keeps things tidy, especially if you have a large number of applications to install.
To remove the source use the following command.
Remove-EventLog -Source "Documentum_Webtop-AddIn_1.0_x86_R01"