💡 Today I Learned

How to pass an argument to a powershell script

For named parameters, first line in the script has to be a param declaration:

param([string]$comment)

or to declare multiple named parameters

param(
	[string]$comment,
	[int32]$LicenseID
)

Then you can do validation and handle gracefully, for example

if ($comment -eq "") {
	write-host "you must give a comment"
	exit
}

A simple if brutal way to bail if a required argument was not specified

param ( [string]$comment = $(throw "Please specify a comment" ))

Can also use a type of boolean parameter called a switch

Param([switch]$IsGood)

Then $IsGood will be $false, unless the parameter was specified

".\script1.ps1"                 #  $IsGood = $false
".\script1.ps1 -IsGood"         #  $IsGood = $true
".\script1.ps1 -isGood:$true"   #  $IsGood = $true
".\script1.ps1 -isGood:$false"  #  $IsGood = $false

Don't like named parameters? Fine! Use positional

$name=$args[0]
$height=$args[1]

...like it's 1999.

Validate the parameters

But if you do use real params you can also enforce simple validation:

For example -- string, length from 1 to 10...

Param(
	[ValidateLength(1,10)][string]$mystring
)

Or how about a number that must be within a range...

Param(
	[ValidateRange(0,10)][int]$myinteger
)

What about -- a filename that must be an existing file...

Param(
	[ValidateScript({Test-Path $_})][string]$smolibrary
)

Source

See also