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

User · Answer

You guys are making this too hard   PowerShell handles this quite elegantly e g     gt   str1    null  gt  if   str1     not empty    else    empty    empty   gt   str2       gt  if   str2     not empty    else    empty    empty   gt   str3        gt  if   str3     not empty    else    empty    not empty   gt   str4    asdf   gt  if   str4     not empty    else    empty    not empty   gt  if   str1 -and  str2     neither empty    else    one or both empty    one or both empty   gt  if   str3 -and  str4     neither empty    else    one or both empty    neither empty

User · Answer

cases  x   null  x       x          test if   x -and  x trim      not empty   else   empty   or if   string   IsNullOrWhiteSpace  x     empty   else   not empty

User · Answer

PowerShell 2 0 replacement for  string   IsNullOrWhiteSpace   is string -notmatch   S      S    any non-whitespace character    gt   null  -notmatch   S  True  gt         -notmatch   S  True  gt    x    -notmatch   S  False   Performance is very close    gt  Measure-Command  1  1000000      string   IsNullOrWhiteSpace          TotalMilliseconds   3641 2089   gt  Measure-Command  1  1000000           -notmatch   S    TotalMilliseconds   4040 8453

User · Answer

You can use the IsNullOrEmpty static method    string   IsNullOrEmpty

User · Answer

An extension of the answer from Keith Hill  to account for whitespace    str    quot       quot  if   str -and  version Trim      Write-Host  quot Not Empty quot    else   Write-Host  quot Empty quot     This returns  quot Empty quot  for nulls  empty strings  and strings with whitespace  and  quot Not Empty quot  for everything else

User · Answer

I have a PowerShell script I have to run on a computer so out of date that it doesn t have  String   IsNullOrWhiteSpace    so I wrote my own   function IsNullOrWhitespace  str        if   str                return   str -replace 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

User · Answer

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

User · Answer

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

User · Answer

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     gt True  val                -eq    0   -f  val  Trim     gt True  val          -eq    0   -f  val  Trim     gt True  val    not null or empty or whitespace      -eq    0   -f  val  Trim     gt 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

User · Answer

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

User · Answer

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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