Better parameter error handling; and better parameter parsing/handling? - parsing

Question

I have a script like this:
param(
[Alias('a')]
[string]$aval,
[Alias('b')]
[switch]$bval,
[Alias('c')]
[string]$cval
)
if($aval.length -gt 1)
{
Do-Something
}
elseif($bval)
{
Do-Something-Else
}
elseif($cval.length -gt 1)
{
Do-Another-Thing
}
else
{
Do-This
}
If someone calls my script like so, an ugly error is displayed saying it is missing an argument for parameter 'aval/bval/cval':
PS C:\> .\MyScript.ps1 -a
C:\MyScript.ps1 : Missing an argument for parameter 'aval'. Specify a
parameter of type 'System.String' and try again.
At line:1 char:18
+ .\MyScript.ps1 -n <<<<
+ CategoryInfo : InvalidArgument: (:) [MyScript.ps1], ParameterBindingException
+ FullyQualifiedErrorId : MissingArgument,MyScript.ps1
Is there any way to make a cleaner, possibly one line, error appear instead? Also, is there a better way to handle parameters then a list of elseif statements (my actual script has ~10 parameters)?
The script sometimes passes an argument with a parameter as well:
EX:
PS C:\> .\MyScript.ps1 -b ServerName
Thanks for any help!

Answer 1

There are a few things that you can look at here. First, if the parameter will never have an associated value and you just want to know if the script was called with the parameter or not, then use a [switch] parameter instead of a string.
Here is a very simple example of using a switch parameter:
param(
[switch]$a
)
if($a){
'Switch was present'
}else{
'No switch present'
}
Save that as a script and run it with and without the -a parameter.
If you will sometimes have the parameter present with some value being passed in but other times without the value, then give the parameter a default value when you define it:
[Alias('a')]
[string]$aval = '',
Then in your logic if something was passed in, the length of the string will be gt 1.
As for the if-then structure that you have, there are a plethora of options for handling this sort of logic. with the little bit of information that you have shared, I suspect that using switch structure will be the best plan:
Get-Help about_Switch