How can I check if a string is null or empty in PowerShell?
.NetStringPowershellNull.Net Problem Overview
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.
.Net Solutions
Solution 1 - .Net
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 2 - .Net
You can use the IsNullOrEmpty
static method:
[string]::IsNullOrEmpty(...)
Solution 3 - .Net
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 ($string) { "string is not null or empty" }
Output:
False
string is null or empty
False
string is null or empty
True
string is not null or empty
Solution 4 - .Net
If it is a parameter in a function, you can validate it with ValidateNotNullOrEmpty
as you can see in this example:
Function Test-Something
{
Param(
[Parameter(Mandatory=$true)]
[ValidateNotNullOrEmpty()]
[string]$UserName
)
#stuff todo
}
Solution 5 - .Net
Personally, I do not accept a whitespace ($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
Solution 6 - .Net
PowerShell 2.0 replacement for [string]::IsNullOrWhiteSpace()
is string -notmatch "\S"
("\S" = any non-whitespace character)
> $null -notmatch "\S"
True
> " " -notmatch "\S"
True
> " x " -notmatch "\S"
False
Performance is very close:
> Measure-Command {1..1000000 |% {[string]::IsNullOrWhiteSpace(" ")}}
TotalMilliseconds : 3641.2089
> Measure-Command {1..1000000 |% {" " -notmatch "\S"}}
TotalMilliseconds : 4040.8453
Solution 7 - .Net
I have a PowerShell script I have to run on a computer so out of date that it doesn't have [String]::IsNullOrWhiteSpace(), so I wrote my own.
function IsNullOrWhitespace($str)
{
if ($str)
{
return ($str -replace " ","" -replace "`t","").Length -eq 0
}
else
{
return $TRUE
}
}
Solution 8 - .Net
# cases
$x = null
$x = ''
$x = ' '
# test
if ($x -and $x.trim()) {'not empty'} else {'empty'}
or
if ([string]::IsNullOrWhiteSpace($x)) {'empty'} else {'not empty'}
Solution 9 - .Net
Another way to accomplish this in a pure PowerShell way would be to do something like this:
("" -eq ("{0}" -f $val).Trim())
This evaluates successfully for null, empty string, and whitespace. I'm formatting the passed value into an empty string to handle null (otherwise a null will cause an error when the Trim is called). Then just evaluate equality with an empty string. I think I still prefer the IsNullOrWhiteSpace, but if you're looking for another way to do it, this will work.
$val = null
("" -eq ("{0}" -f $val).Trim())
>True
$val = " "
("" -eq ("{0}" -f $val).Trim())
>True
$val = ""
("" -eq ("{0}" -f $val).Trim())
>True
$val = "not null or empty or whitespace"
("" -eq ("{0}" -f $val).Trim())
>False
In a fit of boredom, I played with this some and made it shorter (albeit more cryptic):
!!(("$val").Trim())
or
!(("$val").Trim())
depending on what you're trying to do.
Solution 10 - .Net
Note that the "if ($str)"
and "IsNullOrEmpty"
tests don't work comparably in all instances: an assignment of $str=0
produces false for both, and depending on intended program semantics, this could yield a surprise.
Solution 11 - .Net
An extension of the answer from Keith Hill (to account for whitespace):
$str = " "
if ($str -and $version.Trim()) { Write-Host "Not Empty" } else { Write-Host "Empty" }
This returns "Empty" for nulls, empty strings, and strings with whitespace, and "Not Empty" for everything else.
Solution 12 - .Net
You can use a conditional statement with both IsNullOrWhitespace()
and isNullOrEmpty()
static methods testing for white spaces or a null value. For example, before inserting into a MySQL
database, I loop through the values I will enter and use the condition to avoid null or whitespace values.
// RowData is iterative, in this case a hashtable,
// $_.values targets the values of the hashtable
```PowerShell
$rowData | ForEach-Object {
if(-not [string]::IsNullOrEmpty($_.values) -and
-not [string]::IsNullOrWhiteSpace($_.values)) {
// Insert logic here to use non-null/whitespace values
}
}
Solution 13 - .Net
Somewhat related hack - you can exclude empty values (eg Excel has a habit of including an extra empty cell when copying into PowerShell) like this:
get-clipboard | ? {$_}