TOPIC

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