You're looking for PSCmdlet.SessionState.
I solved this same problem by creating a small bridge class, MyCmdlet that all my own cmdlets derive from, and it contains helpers that manage the session state, along with the definition of the object that holds the things you want to persist. In this case I'll just make up some simple things like a username and a database name.
// In MyCmdlet.cs
public class MyStateInfo {
public string Username { get; set;}
public string DbName { get; set;}
}
protected abstract class MyCmdlet : PSCmdlet {
private const string StateName = "_Blah";
protected MyStateInfo getState()
{
if ( ! SessionState.PSVariable.GetValue(StateName, null) is MyStateInfo s))
SessionState.PSVariable.Set(StateName, s = new MyStateInfo());
return s;
}
}
At this point all your cmdlets should inherit from MyCmdlet, and getState() will always return an existing or new variable: changes to the class persist in that same session.
There are probably lots of ways to integrate this in your overall cmdlet parameter design, and this is still kinda new to me so I'm not sure if it's a best practice, but I've solved it by creating a helper cmdlet to set the initial values:
[Cmdlet(VerbsCommon.Set, "MyUsername")]
public class Set_MyUsername : MyCmdlet {
[Parameter(Mandatory = true, Position = 1)]
public string Username {get; set; }
protected override void ProcessRecord()
{
base.ProcessRecord();
WriteVerbose($"Saving {Username} in session state");
getState().Username = Username;
}
}
Then some later cmdlet needs to do something with that:
[Cmdlet(VerbsCommunication.Connect, "Database")]
public class Connect_Database : MyCmdlet {
[Parameter(Mandatory = false)]
public string Username { get; set; }
// other parameters here
protected override void BeginProcessing()
{
base.BeginProcessing();
if (Username == null)
Username = getState().Username;
if (Username == null)
{ // ERROR HERE: missing username }
}
// more stuff
}
Then, your Connect-Database will take an explicit -Username steve parameter (not consulting or touching session state), but without that parameter it pulls it from your session state object. If the username is still missing after this, it fails (probably by ThrowTerminatingError).
Your Select-Project could work the same way.
I usually provide a Get-MyState cmdlet that just writes the state object to the pipeline output, mainly for debugging. You're not limited to just one variable if your application warrants separating these things.
