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Build a variable name

Answered Build a variable name

  • Monday, February 25, 2013 6:49 PM
     
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    I have a script

    [xml]$XmlData = Get-Content $XmlDataFile
$Data = $XmlData.TData.Type18.Job | %{
	New-Object PSObject -Property @{
		id		= $_.id
		DataSetName	= $_.DataSetName
		Job	= $_.Job
	}
}

    This works fine.

    However I want to be able to "build" the variable name, IE

    [xml]$XmlData = Get-Content $XmlDataFile
$Number=18
$VarName = "XmlData.TData.Type"+$Number+".Job"
$Data = $($VarName) | %{
	New-Object PSObject -Property @{
		id		= $_.id
		DataSetName	= $_.DataSetName
		Job	= $_.Job
	}
}

    And get the same results.  I can't seem to get the syntax right.  Can anyone steer me in the right direction?



    • Edited by DennisT. _ Monday, February 25, 2013 6:50 PM
    • Edited by DennisT. _ Monday, February 25, 2013 6:51 PM fix typos
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All Replies

  • Monday, February 25, 2013 7:19 PM
     
     
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    I'm a bit confused here. what, precisely, does the assignment statement send to the pipeline?

    It also seems that you do not want to "build a variable name", but "make the name of a property in a property reference variable". Thinking the latter, I think you need to consider invoke-expression. Take note of example 1 here: help invoke-expression -detailed.

    Al Dunbar -- remember to 'mark or propose as answer' or 'vote as helpful' as appropriate.

     
  • Monday, February 25, 2013 7:22 PM
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    (get-variable variableName).Value

    might get you where you need to go.

    Bill

     
  • Monday, February 25, 2013 8:01 PM
     
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    The xml file contents would be something like this:

    <?xml version="1.0" standalone="yes"?>
<TData>
	<Type18>
		<Host id="System1">
			<DataSetName>SYS1</DataSetName>
			<Job>COPY</Job>
		</Host>
		<Host id="System2">
			<DataSetName>SYS2</DataSetName>
			<Job>MOVE</Job>
		</Host>
		<Host id="System3">
			<DataSetName>SYS3</DataSetName>
			<Job>PURGE</Job>
		</Host>
	</Type18>
</TData>

    The script (slight error in my original script corrected here):

    [xml]$XmlData = Get-Content $XmlDataFile
$Data = $XmlData.TData.Type18.Host | %{
	New-Object PSObject -Property @{
		id		= $_.id
		DataSetName	= $_.DataSetName
		Job	= $_.Job
	}
}

    creates a object with the contents of the xml data in an array, IE $Task[0].Job is "COPY"

    I need to dynamically create the XmlData.TData.Type18.Host string and use it as a reference to access the data it represents.    I've tried get-variable (says it isn't a variable).  I tried invoke-expression but haven't been able to get any results (not really sure how it would work in this case).

     
  • Monday, February 25, 2013 8:01 PM
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    Any time I've started down that path, it always got easier when I gave up on that idea and used a hash table instead.....

    [string](0..33|%{[char][int](46+("686552495351636652556262185355647068516270555358646562655775 0645570").substring(($_*2),2))})-replace " "

     
  • Monday, February 25, 2013 8:10 PM
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    This worked for me:

    [Xml] $XmlData = Get-Content $XmlDataFile
$number = 18
$typeString = "Type{0}" -f $number
$XmlData.TData.$typeString.Host | %{
  New-Object PSObject -Property @{
    id = $_.id
    DataSetName = $_.DataSetName
    Job = $_.Job
  }
}

    Bill

     
  • Monday, February 25, 2013 8:40 PM
     
     
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    If I do the above I don't get any results, IE $Data[0].Job returns nothing.  (I assume you meant $Data = $XmlData.TData.$typeString.Host | %{ )
     
  • Monday, February 25, 2013 8:46 PM
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    That is correct. My script example output the object directly for purposes of demonstrating that it works. If you need to store the object in a variable, by all means, feel free to do that.

    Bill

     
  • Monday, February 25, 2013 8:52 PM
     
     
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    Using the xml data I posted above I get:

    id                                                            DataSetName                                          Job                                                          
    --                                                            -----------                                                   ---

    and no actual data

    If I use $XmlData.TData.Type18.Host instead I get:

    id                                                            DataSetName                                                   Job                                                          
    --                                                            -----------                                                   ---                                                          
    System1                                                       SYS1                                                          COPY                                                         
    System2                                                       SYS2                                                          MOVE                                                         
    System3                                                       SYS3                                                          PURGE

     
  • Monday, February 25, 2013 9:11 PM
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    I copied and pasted your XML data and saved it to C:\Temp\test.xml

    Next I created a PowerShell script file, C:\Temp\test.ps1, that contains only the following lines:

    $XmlDataFile = "C:\Temp\Test.xml"
[Xml] $XmlData = Get-Content $XmlDataFile
$number = 18
$typeString = "Type{0}" -f $number
$XmlData.TData.$typeString.Host | foreach-object {
  New-Object PSObject -Property @{
    id = $_.id
    DataSetName = $_.DataSetName
    Job = $_.Job
  }
}

    Finally, I ran the script from the PowerShell prompt to see its output:

    PS C:\> C:\Temp\test.ps1 | format-list
id          : System1
DataSetName : SYS1
Job         : COPY

id          : System2
DataSetName : SYS2
Job         : MOVE

id          : System3
DataSetName : SYS3
Job         : PURGE

    I piped to format-list, but that only formats the output; it does not change the output.

    All I did was write a very short script that demonstrates a sample of how to accomplish your goal. You can use the same technique I used in this demo script in your own script.

    Bill

     
  • Monday, February 25, 2013 9:35 PM
     
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    Bill,

    Got it!  I wasn't using the foreach.

    I did some testing using hashtables.  Something I hadn't used in powershell before.  I found the following seems to work and is definitely shorter:

    [xml]$XmlData = (Get-Content $XmlDataFile)
    $Num=18
$TypeStr="Type"+$Num
$Data=$XmlData.TData.$TypeStr.SelectNodes("//Host")