How do I check that a string contains a date?

Question

My script's input parameter is a date or a number. Here's a script that works fine, so you can see what I am trying to do:

param($date = (Get-Date))

if ($date -match "^\d+$")
{  
    $date = (Get-Date).AddDays($date)
} 
elseif ($date -as [DateTime]) 
{
    $date = [DateTime]::Parse($date)  
}
else 
{  
    'You entered an invalid date'
    exit 1
}

Here's my previous attempt that does not work:

param($date = (Get-Date))

if ($date -as [DateTime]) 
{
    $date = [DateTime]::Parse($date)  
}
elseif ($date -match "^\d+$")
{  
    $date = (Get-Date).AddDays($date)
} 
else 
{  
    'You entered an invalid date'
    exit 1
}

When I input a number, the script breaks at date parsing line. It looks like my "is is date" check returns true when given a number.

Is it a bug? Is it by design?

Answer 1

This is a short alternative:

function isDate([string]$strdate)
{
    [boolean]($strdate -as [DateTime])
}