How to require command-line arguments (not parameters) in the PowerShell?

Question

Different from: How to handle command-line arguments in PowerShell

What's the best way to handle an unnamed command-line argument in a powershell script?

For example, I have a powershell script that I would like to run as

.\test.ps1 L3

and have an error if L3 is not supplied. I don't want to have to run it as:

.\test.ps1 -lab L3

My current script:

$args[0]

does not cause an error if the argument is omtted.

This looks promising, haven't tried it yet: https://technet.microsoft.com/en-us/library/hh847743.aspx * Edit: * The promising link is useful -- I used it to form all my examples

Why don't you want named arguments (parameters)? They make for much more readable code, and if you set up your parameters properly I think you can leave them unnamed when you pass them in, as long as you do it in the right order. — alroc
– alroc, Commented Feb 26, 2015 at 14:42
Named arguments are great. But this script ALWAYS requires this argument and it will save three-four keystrokes every time I use it. — Josiah Yoder
– Josiah Yoder, Commented Feb 26, 2015 at 15:08
If it's the only argument, you can make it named and pass it in un-named and PowerShell will handle it just fine. Don't write for your convenience - write to make your script understandable for the next person who has to use it and isn't you. — alroc
– alroc, Commented Feb 26, 2015 at 15:11
My point remains. Even at the command line, write for the understanding of the next person, not for your convenience. Named parameters are almost always a good thing, regardless - when someone has to modify this script to add another parameter, they'll want them named. It costs you nothing to make it named now, just do it. — alroc
– alroc, Commented Feb 26, 2015 at 15:29
This seems like a potentially contentious point. Perhaps it's just my bash background, but I find unnamed parameters for one or two essential arguments to be perfectly readable in many cases. Perhaps this is an exception. — Josiah Yoder
– Josiah Yoder, Commented Feb 26, 2015 at 15:41

Josiah Yoder · Accepted Answer · 2015-02-26 15:38:42Z

4

This did the trick:

Param
  (
     [parameter(Position=0, Mandatory=$true)]
     [String]
     $LabNumber
  ) 

$LabNumber

This second option is interesting, but I prefer the Mandatory=$true above, because it will actually prompt you to enter it if you forget it.

Param
  (
     [parameter(Position=0)]
     [String]
     $LabNumber=$(throw "LabNumber is required.  Usage Example: .\test.ps1 L3")
  ) 

$LabNumber

And, as @alroc prefers for all parameters, the second parameter must be named:

Param
  (
     [parameter(Position=0, Mandatory=$true)]
     [String]
     $LabNumber,

     [alias("Submissions")] 
     [String]
     $LoginsFilename = "..\logins.txt"
  )
"LabNumber:"+$LabNumber
"LoginsFilename:"+$LoginsFilename

edited Feb 26, 2015 at 15:38

answered Feb 26, 2015 at 14:11

Josiah Yoder

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