Flexible pipelining with ScriptBlock Parameters

re: Flexible pipelining with ScriptBlock Parameters

jvierra — Sat, 24 Jun 2006 04:22:41 GMT

Now that is going to come in very handy as we move along.

PS amazes me more-an-more eac day. Keep up the exceellent blogs Jeffery/PS-Team.

re: Flexible pipelining with ScriptBlock Parameters

dontBotherMeWithSpam — Sat, 24 Jun 2006 17:44:09 GMT

I think you have forgotten to mention one of the most important(well in my personal opinion that is) that when you use "scriptblock parameter", only one instance of cmdlet is run while one or more instances are run when using "foreach"... Did i get that correct?

Ah, another one, I am not sure if I am remembering this correct that, there is a gotcha when it comes to passing a script block as a parameter that, you can't use scriptblock parameter on a parameter which accepts an object of type PSObject.(is it also a case for PSCustomObjects?)

re: Flexible pipelining with ScriptBlock Parameters

PowerShellTeam — Sun, 25 Jun 2006 07:59:55 GMT

> only one instance of cmdlet is run while one or more instances are run when using "foreach"...

That is absolutely correct and you are also correct that this can be a critical difference. Imagine the case where a Cmdlet opens a DB connections, puts each object into the DB and then closes the connection. If this Cmdlet is in a foreach block - it will open and close the connection for every object where as using ScriptBlock parameters, you only have 1 instance of the Cmdlet so it opens and closes the connection once.

Correct as well on the restriction. Scriptblocks work on parameters which are not of type SCRIPTBLOCK or OBJECT. I haven't looked at the code but I don't believe that there is a problem with PSObject types.

Jeffrey Snover
Windows PowerShell Architect

re: Flexible pipelining with ScriptBlock Parameters

Boris Verkhovykh — Mon, 26 Jun 2006 17:06:26 GMT

Maybe not the right place for this question, but this is the most close topic to my current problem.
I have created own cmdlet, which works fine in the defautl PowerShell host. It accepts various parameters from command line and the "target" item names from the pipeline.
Now I am trying to create custom PS Host application. And here I cannot supply a list of "target" objects - I always get parameter binding exceptions.
SDK is almost empty... Could you help me?

re: Flexible pipelining with ScriptBlock Parameters

dontBotherMeWithSpam — Mon, 26 Jun 2006 19:44:28 GMT

> Imagine the case where a Cmdlet opens a DB connections, puts each object into the DB and then closes the connection

Ah, now that's a case I have never though of where I could make use of this feature!

Thank you for clearing up there and for the post, Jeffrey.

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