{"id":1355,"date":"2012-06-19T00:00:00","date_gmt":"2012-06-19T00:00:00","guid":{"rendered":"https:\/\/test.simple-talk.com\/uncategorized\/the-posh-dba-the-attributes-of-advanced-functions\/"},"modified":"2021-08-24T13:40:10","modified_gmt":"2021-08-24T13:40:10","slug":"the-posh-dba-the-attributes-of-advanced-functions","status":"publish","type":"post","link":"https:\/\/www.red-gate.com\/simple-talk\/databases\/sql-server\/database-administration-sql-server\/the-posh-dba-the-attributes-of-advanced-functions\/","title":{"rendered":"The PoSh DBA – The Attributes of Advanced Functions"},"content":{"rendered":"

PowerShell advanced functions provide some powerful magic. In the previous article<\/a> we covered some “features” that can help us to write better code, and now we are going to focus in on the magic of those features that are to do with the parameters that we pass to advanced functions.<\/p>\n

We already know that, when we put the [CmdletBinding()]<\/code> attribute in a function, it changes it into an advanced function, thereby allowing options that you don’t have in normal functions – see The PoSh DBA: Grown-Up PowerShell Functions<\/a>. What I didn’t emphasize then is that all magic comes at a price. In this case, the price is that you must write code that uses the magic correctly; you must be more precise and cautious, just like any magician. To start with, the function’s parameters should be formally defined. We lose something by this: When we write a function without the [CmdletBinding()]<\/code> attribute, we can be less strict, and pass more parameters than we have defined in the function, because the $args<\/code> variable stores them.<\/p>\n

function ILoveInformalParameters { \r\n        param ($IamFirst,$IamSecond)\r\n        Write-Host \"I am The First Parameter : $($IamFirst)\"\r\n        Write-Host \"I am The Second Parameter : $($IamSecond)\"\r\n        Write-Host \"And I am The Rest : $($args)\"\r\n        \r\n    }<\/pre>\n
If we now call our informal function :<\/p>\n
ILoveInformalParameters ObiWanKenoby Yoda DarthVader DarthSidious\r\n\r\n\r\nI am The First Parameter : ObiWanKenoby\r\nI am The Second Parameter : Yoda\r\nAnd I am The Rest : DarthVader DarthSidious\r\n<\/pre>\n
But if, without due thought, we add just the [CmdletBinding()]<\/code> attribute to this without any option…<\/p>\n
function ILoveInformalParameters { \r\n       [cmdletbinding()]\r\n       param ($IamFirst,$IamSecond)\r\n       .......    \r\n   }<\/pre>\n
…And try to run it using more parameters than we’ve declared…<\/p>\n
ILoveInformalParameters ObiWanKenoby Yoda DarthVader DarthSidious \r\n\r\nILoveInformalParameters : A positional parameter cannot be found that accepts argument 'DarthVader'....... <\/pre>\n
Yes. It is an error in the positional parameters. You’ve just dropped the rabbit from the hat.<\/p>\n
The CmdletBinding arguments<\/h3>\n
There are 3 arguments that are concerned with the parameters that can be passed to PowerShell functions. These are :<\/p>\n