How do I negate a condition in PowerShell?

Question

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 · Accepted Answer · 2014-05-19T23:56:34.970

656

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!"}

edited May 19 '14 at 23:56

answered Nov 11 '11 at 14:54

Rynant

2

Interesting, so `-not` comes with the traditional alternative of `!` then? Can I somehow get the traditional alternatives for `-eq` and `-ne` too? – Roman Starkov Dec 07 '12 at 18:04
9

No, `-not` is the only logical operator that comes with an alternate (see `help about_Logical_Operators`), and operators cannot be aliased. – Rynant Dec 07 '12 at 21:08
21

Thanks, I was missing fact that the use of `!` required parentheses. – Holistic Developer Oct 17 '14 at 18:43
11

_The term '!Test-Path' is not recognized as the name of a cmdlet ..._ :) – sodawillow Dec 05 '15 at 12:57
I wish there were a better way that supported piping. E.g. `Get-ChildItem -r -inc *.txt | !Test-Path` – Neil Barnwell May 20 '19 at 14:53
1

"Just for fun" - it's all fun until we come back to our code 6 months later. – Hannes Schneidermayer Oct 11 '21 at 11:51

score 13 · Answer 2 · edited Nov 24 '21 at 20:39

13

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...

edited Nov 24 '21 at 20:39

ssilas777

answered Jul 05 '19 at 21:36

ZEE

Zombo · Answer 3 · 2014-08-18T16:46:05.170

10

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!'}

edited Aug 18 '14 at 16:46

answered May 19 '14 at 00:50

Zombo

1

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](http://stackoverflow.com/q/31888580/450913). – orad Aug 13 '15 at 13:06
2

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. – David A. Gray May 30 '18 at 06:44
1

@DavidA.Gray Ruby has `unless` as keyword (just like `if`) but most user from other languages hate it. – Franklin Yu Nov 27 '18 at 05:09

score 6 · Answer 4 · answered May 08 '20 at 11:50

6

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!"
}

answered May 08 '20 at 11:50

Melchior

4 Answers4