about_Scripting_ValidateScript.help.txt
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about_Scripting_ValidateScript SHORT DESCRIPTION A tutorial on validating a parameter value with a short scriptblock. LONG DESCRIPTION Sometimes validating a parameter value can get a little complex. However, we can use PowerShell to assist in the validation effort by running the parameter value through a short script. Well, technically a scriptblock. To use this attribute we’ll insert a scriptblock inside the parentheses. The scriptblock can be as complicated as you need it to be, but it must evaluate to either True or False. Use $_ to indicate the parameter value. So using my datetime example, I might use a validation script like this: Param ( [Parameter(Position=0,Mandatory=$True, HelpMessage="Enter a date",ValueFromPipeline=$True)] [ValidateScript( { [datetime]$start="1/1/2012" $end=Get-Date ($_ -ge $start) -AND ($_ -le $end) } )] [datetime]$Date ) Process { write-host $date -ForegroundColor Green } With a validation script I have much more flexibility. Now look at the results: PS C:\Scripts> "2/12/2012","5/1/2012","3/15/2012","12/1/2011", >> "13/2/2012" | .\Demo-ValidateScript-Date.ps1 | clip >> 2/12/2012 12:00:00 AM C:\scripts\Demo-ValidateScript-Date.ps1 : Cannot validate argument on parameter 'Date'. The "[datetime]$start="1/1/2012" $end=Get-Date ($_ -ge $start) -AND ($_ -le $end) " validation script for the argument with value "5/1/2012 12:00:00 AM" did not return true. Determine why the validation script failed and then try the command again. At line:1 char:92 + "2/12/2012","5/1/2012","3/15/2012","12/1/2011","13/2/2012" | . \Demo-ValidateScript-Date.ps1 <<<< | clip + CategoryInfo : InvalidData: (5/1/2012:String) [Demo- ValidateScript-Date.ps1], ParameterBindingValidationException + FullyQualifiedErrorId : ParameterArgumentValidationError,Demo- ValidateScript-Date.ps1 ... C:\scripts\Demo-ValidateScript-Date.ps1 : The input object cannot be bound to any parameters for the command either because the command does not take pipeline input or the input and its properties do not match any of the parameters that take pipeline input. At line:1 char:92 + "2/12/2012","5/1/2012","3/15/2012","12/1/2011","13/2/2012" | .\Demo- ValidateScript-Date.ps1 <<<< + CategoryInfo : InvalidArgument: (13/2/2012:String) [Demo- ValidateScript-Date.ps1], ParameterBindingException + FullyQualifiedErrorId : InputObjectNotBound,Demo-ValidateScript- ate.ps1 The valid dates pass, dates outside the range fail the validation test and the last value which isn’t a legal date also fails but with a slightly different error message. As with all of the validation attributes I could have inserted this code into the body of my script and thrown my own errors. That choice is up to you. [ValidateScript()] isn’t difficult to use. Just remember to insert your commands into a scriptblock, use $_ for the parameter value, and make sure the scriptblock results in either $True or $False. SEE ALSO about_Functions_Advanced_Parameters http://jdhitsolutions.com/blog |