How can I check if a string is null or empty in PowerShell?

Question

Is there a built-in IsNullOrEmpty-like function in order to check if a string is null or empty, in PowerShell?

I could not find it so far and if there is a built-in way, I do not want to write a function for this.

Solution 1

You can use the IsNullOrEmpty static method:

[string]::IsNullOrEmpty(...)

Solution 2

You guys are making this too hard. PowerShell handles this quite elegantly e.g.:

> $str1 = $null
> if ($str1) { 'not empty' } else { 'empty' }
empty

> $str2 = ''
> if ($str2) { 'not empty' } else { 'empty' }
empty

> $str3 = ' '
> if ($str3) { 'not empty' } else { 'empty' }
not empty

> $str4 = 'asdf'
> if ($str4) { 'not empty' } else { 'empty' }
not empty

> if ($str1 -and $str2) { 'neither empty' } else { 'one or both empty' }
one or both empty

> if ($str3 -and $str4) { 'neither empty' } else { 'one or both empty' }
neither empty

Solution 3

In addition to [string]::IsNullOrEmpty in order to check for null or empty you can cast a string to a Boolean explicitly or in Boolean expressions:

$string = $null
[bool]$string
if (!$string) { "string is null or empty" }

$string = ''
[bool]$string
if (!$string) { "string is null or empty" }

$string = 'something'
[bool]$string
if ($string) { "string is not null or empty" }

Output:

False
string is null or empty

False
string is null or empty

True
string is not null or empty

Solution 4

If it is a parameter in a function, you can validate it with ValidateNotNullOrEmpty as you can see in this example:

Function Test-Something
{
    Param(
        [Parameter(Mandatory=$true)]
        [ValidateNotNullOrEmpty()]
        [string]$UserName
    )

    #stuff todo
}

Solution 5

Personally, I do not accept a whitespace ($STR3) as being 'not empty'.

When a variable that only contains whitespaces is passed onto a parameter, it will often error that the parameters value may not be '$null', instead of saying it may not be a whitespace, some remove commands might remove a root folder instead of a subfolder if the subfolder name is a "white space", all the reason not to accept a string containing whitespaces in many cases.

I find this is the best way to accomplish it:

$STR1 = $null
IF ([string]::IsNullOrWhitespace($STR1)){'empty'} else {'not empty'}

Empty

$STR2 = ""
IF ([string]::IsNullOrWhitespace($STR2)){'empty'} else {'not empty'}

Empty

$STR3 = " "
IF ([string]::IsNullOrWhitespace($STR3)){'empty !! :-)'} else {'not Empty :-('}

Empty!! :-)

$STR4 = "Nico"
IF ([string]::IsNullOrWhitespace($STR4)){'empty'} else {'not empty'}

Not empty

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