powershell history: how do you prevent duplicate commands

Answer 1

Get-Unique also requires a sorted list and I assume you probably want to preserve execution order. Try this instead:

Get-History -Count 32767 | Group CommandLine | Foreach {$_.Group[0]} | 
Export-Clixml "$home\pshist.xml"

This approach uses the Group-Object cmdlet to create unique buckets of commands and then the Foreach-Object block just grabs the first item in each bucket.

BTW if you want all commands saved to a history file I would use the limit value - 32767 - unless that is what you set $MaximumHistoryCount to. :-)

BTW if you want to automatically save this on exit you can do this on 2.0 like so:

Register-EngineEvent PowerShell.Exiting {
    Get-History -Count 32767 | Group CommandLine | 
    Foreach {$_.Group[0]} | Export-CliXml "$home\pshist.xml" } -SupportEvent

Then to restore upon load all you need is:

Import-CliXml "$home\pshist.xml" | Add-History