Check if a string is not NULL or EMPTY - powershell

Question

In below code, I need to check if version string is not empty then append its value to the request variable.
if ([string]::IsNullOrEmpty($version))
{
$request += "/" + $version
}
How to check not in if condition?

Answer 1

if (-not ([string]::IsNullOrEmpty($version)))
{
$request += "/" + $version
}
You can also use ! as an alternative to -not.

Answer 2

You don't necessarily have to use the [string]:: prefix. This works in the same way:
if ($version)
{
$request += "/" + $version
}
A variable that is null or empty string evaluates to false.

Answer 3

As in many other programming and scripting languages you can do so by adding ! in front of the condition
if (![string]::IsNullOrEmpty($version))
{
$request += "/" + $version
}

Answer 4

If the variable is a parameter then you could use advanced function parameter binding like below to validate not null or empty:
[CmdletBinding()]
Param (
[parameter(mandatory=$true)]
[ValidateNotNullOrEmpty()]
[string]$Version
)

Answer 5

if (!$variablename)
{
Write-Host "variable is null"
}
I hope this simple answer will resolve the question.
Source

Answer 6

I would define $Version as a string to start with
[string]$Version
and if it's a param you can use the code posted by Samselvaprabu
or if you would rather not present your users with an error you can do something like
while (-not($version)){
$version = Read-Host "Enter the version ya fool!"
}
$request += "/" + $version

Answer 7

You can use the [string]::IsNullOrEmpty($version) method if it is a string.
But, I was looking for a universal way to check nulls (regardless of data type)
in Powershell. Checking for null (or not null) values in
PowerShell is tricky. Using ($value -eq $null) or ($value -ne
$null) does not always work. Neither does if($value). Using them
can even cause problems later on.
Just read this Microsoft article below (IN IT'S ENTIRETY) to get a grasp
of how tricky nulls can be in Powershell.
[https://learn.microsoft.com/en-us/powershell/scripting/learn/deep-dives/everything-about-null?view=powershell-7.1][1]
I wrote these two functions below for checking for null (or not null) values
in PowerShell. I "believe" they should work for any and all values
and data types.
I hope someone finds them helpful.
I am not sure why MS hasn't put something like this into PowerShell natively to
make handling nulls easier (and less dangerous) in PowerShell.
I hope this helps someone.
If anyone knows of an unseen "pitfall" or problem with this method,
please post a comment here so we can know that.
Thanks!
<#
*********************
FUNCTION: ValueIsNull
*********************
Use this function ValueIsNull below for checking for null values
rather using -eq $null or if($value) methods. Those may not work as expected.
See reference below for more details on $null values in PowerShell.
[https://learn.microsoft.com/en-us/powershell/scripting/learn/deep-dives/everything-about-null?view=powershell-7.1][1]
An if statement with a call to ValueIsNull can be written like this:
if (ValueIsNull($TheValue))
#>
function ValueIsNull {
param($valueToCheck)
# In Powershell when a parameter of a function does not have a data type defined,
# it will create the parameter as a PSObject. It will do this for
# an object, an array, and a base date type (int, string, DateTime, etc.)
# However if the value passed in is $null, then it will still be $null.
# So, using a function to check null gives us the ability to determine if the parameter
# is null or not by checking if the parameter is a PSObject or not.
# This function could be written more efficiently, but intentionally
# putting it in a more readable format.
# Special Note: This cannot tell the difference between a parameter
# that is a true $null and an undeclared variable passed in as the parameter.
# ie - If you type the variable name wrong and pass that in to this function it will see it as a null.
[bool]$returnValue = $True
[bool]$isItAnObject=$True
[string]$ObjectToString = ""
try { $ObjectToString = $valueToCheck.PSObject.ToString() } catch { $isItAnObject = $false }
if ($isItAnObject)
{
$returnValue=$False
}
return $returnValue
}
<#
************************
FUNCTION: ValueIsNotNull
************************
Use this function ValueIsNotNull below for checking values for
being "not-null" rather than using -ne $null or if($value) methods.
Both may not work as expected.
See notes on ValueIsNull function above for more info.
ValueIsNotNull just calls the ValueIsNull function and then reverses
the boolean result. However, having ValueIsNotNull available allows
you to avoid having to use -eq and\or -ne against ValueIsNull results.
You can disregard this function and just use !ValueIsNull($value).
But, it is my preference to have both for easier readability of code.
An if statement with a call to ValueIsNotNull can be written like this:
if (ValueIsNotNull($TheValue))
#>
function ValueIsNotNull {
param($valueToCheck)
[bool]$returnValue = !(ValueIsNull($valueToCheck))
return $returnValue
}
You can use the following list of calls to ValueIsNull to test it out.
$psObject = New-Object PSObject
Add-Member -InputObject $psObject -MemberType NoteProperty -Name customproperty -Value "TestObject"
$valIsNull = ValueIsNull($psObject)
$props = #{
Property1 = 'one'
Property2 = 'two'
Property3 = 'three'
}
$otherPSobject = new-object psobject -Property $props
$valIsNull = ValueIsNull($otherPSobject)
# Now null the object
$otherPSobject = $null
$valIsNull = ValueIsNull($otherPSobject)
# Now an explicit null
$testNullValue = $null
$valIsNull = ValueIsNull($testNullValue)
# Now a variable that is not defined (maybe a type error in variable name)
# This will return a true because the function can't tell the difference
# between a null and an undeclared variable.
$valIsNull = ValueIsNull($valueNotDefine)
[int32]$intValueTyped = 25
$valIsNull = ValueIsNull($intValueTyped)
$intValueLoose = 67
$valIsNull = ValueIsNull($intValueLoose)
$arrayOfIntLooseType = 4,2,6,9,1
$valIsNull = ValueIsNull($arrayOfIntLooseType)
[int32[]]$arrayOfIntStrongType = 1500,2230,3350,4000
$valIsNull = ValueIsNull($arrayOfIntStrongType)
#Now take the same int array variable and null it.
$arrayOfIntStrongType = $null
$valIsNull = ValueIsNull($arrayOfIntStrongType)
$stringValueLoose = "String Loose Type"
$valIsNull = ValueIsNull($stringValueLoose)
[string]$stringValueStrong = "String Strong Type"
$valIsNull = ValueIsNull($stringValueStrong)
$dateTimeArrayLooseValue = #("1/1/2017", "2/1/2017", "3/1/2017").ForEach([datetime])
$valIsNull = ValueIsNull($dateTimeArrayLooseValue)
# Note that this has a $null in the array values. Still returns false correctly.
$stringArrayLooseWithNull = #("String1", "String2", $null, "String3")
$valIsNull = ValueIsNull($stringArrayLooseWithNull)