about_Scripting_ValidatePattern.help.txt
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about_Scripting_ValidatePattern SHORT DESCRIPTION A tutorial on validating a parameter value based on a regular expression pattern match. LONG DESCRIPTION This topic will cover using a regular expression pattern to validate a parameter value. I’m going to assume you have a rudimentary knowledge of how to use regular expressions in PowerShell. If not, there is an entire chapter devoted to the topic in Windows PowerShell 2.0: TFM by Don Jones and Jeffery Hicks (SAPIEN Press). The parameter attribute is [ValidatePattern()]. Inside the parentheses you place a scriptblock with the regular expression pattern. For example, in PowerShell we might write a command like this to verify if something is a number of 1 to 3 digits.: $x -match "^\d{1,3}$" To use that pattern in a [ValidatePattern()] attribute, you would write it like this: [ValidatePattern({^\d{1,3}$})] There is no need to use the -match operator or $_. Sure, I suppose you could write a validation script to achieve the same effect, but this is just as easy. I recommend testing your pattern from the PowerShell prompt, especially testing for failures. Here’s a more complete example. Param ( [Parameter(Position=0,Mandatory=$True, HelpMessage="Enter a UNC path like \\server\share")] [ValidatePattern({^\\\\\S*\\\S*$})] [ValidateScript({Test-Path -Path $_ })] [string]$Path ) Write-Host "Getting top level folder size for $Path" -ForegroundColor Red dir $path | measure-object -Property Length -sum For you regular expression gurus, don’t get hung up on my pattern. It works for my illustration purposes. Your pattern can be as simple or as complex as you need it to be. In this short script I’m expecting a path value like \\file01\public. If the value is not in this format, the pattern validation will fail, PowerShell will throw an exception and the script will fail. Notice I’m also using a second parameter validation attribute, [ValidateScript()]. It is possible for the pattern to be correct but invalid so I can combine both validation tests. PS C:\Scripts\> .\Demo-ValidatePattern.ps1 '\\file01\temp' C:\scripts\Demo-ValidatePattern.ps1 : Cannot validate argument on para meter 'Path'. The "Test-Path -Path $_ " validation script for the argu ment with value "\\file01\temp" did not return true. Determine why the validation script failed and then try the command again. At line:1 char:28 + C:\Scripts\Demo-ValidatePattern.ps1 <<<< '\\file01\temp' + CategoryInfo : InvalidData: (:) [Demo-ValidatePattern.ps 1], ParameterBindingValidationException + FullyQualifiedErrorId : ParameterArgumentValidationError,Demo-Vali datePattern.ps1 The bottom line is that any regular expression pattern you can use with the -match operator should work with this validation attribute. SEE ALSO about_Functions_Advanced_Parameters about_Regular_Expressions about_Comparison_Operators http://jdhitsolutions.com/blog |