What's the Value of an Empty Array?

s31064 · 2018-08-03T15:17:48.000Z

I’m having a problem with the error routines I’m trying to rewrite for some scripts. The error codes are captured to arrays, and then used as parameters in if statements for reporting. If there are errors, then all is fine, but if everything works OK in the processes, the reporting errors out. I think I’ve determined that the problem is the way I’m testing the arrays, but I’m not sure. I came up with this quick script to test the value of an empty array, and it leads me to believe there’s something special about an empty array.

$SkippedFiles = @()
if ($SkippedFiles -eq 0)
{
  Write-Host 'Empty arrays = 0'
} 
elseif ($SkippedFiles -eq $null) 
{
  Write-Host 'Empty arrays = $null'
} 
else 
{
  Write-Host 'Empty arrays are neither $null nor 0'
}

The answer I get is (you guessed it)

Empty arrays are neither $null nor 0

So just what is the value of an empty array and how do you test for it?

Neally · 2018-08-03T15:23:41.000Z

You can just try

$SkippedFiles = @()
if ($SkippedFiles) {
    Write-Host 'Not empty'
} 
else {
    Write-Host 'Empty arrays'
}

IF will check if it is null or empty

Why are you trying to differentiate? Either way the array is empty.
Its an array, so you’re looking for Count to test for contents.

Maybe I’m not understanding correctly, sorry.

dancrane · 2018-08-03T15:43:22.000Z

Neally:

You can just try
$SkippedFiles = @()
if ($SkippedFiles) {
    Write-Host 'Not empty'
} 
else {
    Write-Host 'Empty arrays'
}
IF will check if it is null or empty

Why are you trying to differentiate? Either way the array is empty.
Its an array, so you’re looking for Count to test for contents.

Maybe I’m not understanding correctly, sorry.

The converse of this being if you want to check for the absence of contents you can simply do a

If !($TestedVariable) {
    Do things
}
Else {
    other things when the array isn't empty
}

s31064 · 2018-08-03T15:49:08.000Z

Neally:

IF will check if it is null or empty

Maybe I’m not understanding correctly, sorry.

Sometimes the obvious is too obvious. Whenever I IF something I’m thinking of a comparison. I tend to forget it can also just check for the existence of something (which I guess IS a comparison, of a sort).

To verify what you said, I wrote another quick test:

$SkippedFiles = @()
if (!($SkippedFiles))
{
  Write-Host 'Empty arrays do not really exist'
} 
elseif ($SkippedFiles) 
{
  Write-Host 'Empty arrays exist'
} 
else 
{
  Write-Host 'Empty arrays are located in the Twilight Zone next to my bonus'
}

Naturally the answer was

Empty arrays do not really exist

This will work out perfectly. Once again you’ve straightened me out. Thanks for the help.

Neally · 2018-08-03T15:54:32.000Z

dancrane:

The converse of this being if you want to check for the absence of contents you can simply do a
If !($TestedVariable) {
    Do things
}
Else {
    other things when the array isn't empty
}

nitpicking:

If !($TestedVariable) {
    'Do things'
}

#should be
If (!$TestedVariable) {
    'Do things'

}

This will be a syntax error as powershell expects an open bracket after the IF

Try to use ‘-not’ rather than ‘!’, makes it easier to read :¬)

PLEASE READ BEFORE POSTING! Read if you're new to the PowerShell forum! Programming & Development

Hi, and welcome to the PowerShell forum! Don’t apologize for being a “noob” or “newbie” or “n00b.” There’s just no need – nobody will think you’re stupid, and the forums are all about asking questions. Just ask! Use a descriptive subject. Don't say "Need help" or "PowerShell Help", actually summarize what the problem is. It helps the rest of us keep track of which problem is which. Don’t post massive scripts. We’re all volunteers and we don’t have time to read all that, nor will we copy, past…

Try to avoid using obscure or punctuation aliases (like ? and %)
use command names instead.

If (-not $TestedVariable) {
    'Do things'
}

s31064 · 2018-08-03T15:54:44.000Z

dancrane:

The converse of this being if you want to check for the absence of contents you can simply do a
If !($TestedVariable) {
    Do things
}
Else {
    other things when the array isn't empty
}

Yeah, that’s the gist of it. Instead of testing for a 0 or $null value, I’m checking to see if it exists now. Thanks for your help.

dancrane · 2018-08-06T09:50:28.000Z

Neally:

snip

Haha, that’s what I get for trying to answer a quick question in the middle of doing a site survey. At least the idea is sound, if not the execution!