How do I negate a condition in PowerShell?

windows powershell

How do I negate a conditional test in PowerShell?

For example, if I want to check for the directory C:\Code, I can run:

if (Test-Path C:\Code){
  write "it exists!"
}

Is there a way to negate that condition, e.g. (non-working):

if (Not (Test-Path C:\Code)){
  write "it doesn't exist!"
}

Workaround:

if (Test-Path C:\Code){
}
else {
  write "it doesn't exist"
}

This works fine, but I'd prefer something inline.

Rynant

You almost had it with Not. It should be:

if (-Not (Test-Path C:\Code)) {
    write "it doesn't exist!"
}

You can also use !: if (!(Test-Path C:\Code)){}

Just for fun, you could also use bitwise exclusive or, though it's not the most readable/understandable method.

if ((test-path C:\code) -bxor 1) {write "it doesn't exist!"}

Interesting, so -not comes with the traditional alternative of ! then? Can I somehow get the traditional alternatives for -eq and -ne too?

No, -not is the only logical operator that comes with an alternate (see help about_Logical_Operators), and operators cannot be aliased.

Thanks, I was missing fact that the use of ! required parentheses.

The term '!Test-Path' is not recognized as the name of a cmdlet ... :)

I wish there were a better way that supported piping. E.g. Get-ChildItem -r -inc *.txt | !Test-Path

Zombo

If you are like me and dislike the double parenthesis, you can use a function

function not ($cm, $pm) {
  if (& $cm $pm) {0} else {1}
}

if (not Test-Path C:\Code) {'it does not exist!'}

Example

I like this, but probably can't use this not implementation everywhere (for example not Test-Path -path C:\Code won't work). See also this related post.

Perl has a more logical, in the Vulcan sense, idiom, called Unless, which is written as a function. Being half Vulcan, I prefer it, and have implemented it in both C#, as a function, and in C and C++, as a macro.

@DavidA.Gray Ruby has unless as keyword (just like if) but most user from other languages hate it.

ssilas777

Powershell also accept the C/C++/C* not operator

 if ( !(Test-Path C:\Code) ){ write "it doesn't exist!" }

I use it often because I'm used to C*... allows code compression/simplification... I also find it more elegant...

Melchior

if you don't like the double brackets or you don't want to write a function, you can just use a variable.

$path = Test-Path C:\Code
if (!$path) {
    write "it doesn't exist!"
}

How do I negate a condition in PowerShell?

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