How to test for an invalid path in powershell?

Question

I have a script that tries to run some executable using a relative path.
So I use test-path to verify that the executable is where it is supposed to be. If not I try another location.

if(test-path "$current../../../myexe.exe"){
   # found it!
}

But in this case, if the $current is C:/folder/ then test-path "C:/folder/../../../myexe.exe" fails with

The path ... referred to an item that was outside the base 'C:'

Is there a clean and sure way to test for a path, so that it returns true or false, and won't throw me some unexpected error?

Community · Accepted Answer · 2017-05-23 11:45:22Z

2

Test-Path ([io.path]::Combine($current,(Resolve-Path ../../../myexe.exe)))

See this thread for more info:

edited May 23, 2017 at 11:45

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answered Apr 9, 2013 at 11:12

Shay Levy

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5 Comments

Stéphane Over a year ago

I just got it to work, I used [IO.File]::Exists() I think that Resolve-Path would throw the same kind of exception

Shay Levy Over a year ago

I wouldn't change the process working directory, leeholmes.com/blog/2006/06/26/…

Stéphane Over a year ago

Interesting, then I should maybe use [IO.Path]::GetFullPath("$pwd\..\..\myexe.exe") to avoid the exception of resolve-path, and then File.Exists to avoir the exception of test-path

Shay Levy Over a year ago

You can use Test-Path instead of the .net class.

Stéphane Over a year ago

ah that's right, because in this case, GetFullPath takes care of the problematic exception.

Stéphane · Accepted Answer · 2013-04-09 12:35:09Z

2

I got it to work using .NET File.Exists, but you have to set the Environment.CurrentDirectory first if you want relative path to be resolved correctly.

EDIT: not changing CurrentDirectory after Shay Levy pointed out that it can be dangerous for other background processes (see http://www.leeholmes.com/blog/2006/06/26/current-working-directory-with-powershell-and-net-calls/ )

~~[Environment]::CurrentDirectory = $pwd~~

[System.IO.File].Exists("$pwd\$invalidRelativePath")
False

edited Apr 9, 2013 at 12:35

answered Apr 9, 2013 at 11:29

Stéphane

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Comments

Mr. Annoyed · Accepted Answer · 2015-06-11 19:57:43Z

Test-path is fundamentally broken.

Even SilentlyContinue is broken:

Test-Path $MyPath -ErrorAction SilentlyContinue

This will still blow up if $MyPath is $null, empty, or doesn't exist as a variable.

It even returns $true if $MyPath is only a space. Where the heck is that " " folder!

Below is a workaround that work for the following situations:

$MyPath = "C:\windows"  #Test-Path return $True as it should
$MyPath = " "       #Test-Path returns $true, Should return $False
$MyPath = ""        #Test-Path Blows up, Should return $False
$MyPath = $null      #Test-Path Blows up, Should return $False
Remove-Variable -Name MyPath -ErrorAction SilentlyContinue  #Test-Path Blows up, Should return $False

The solution lies in forcing it to return $False when Test-Path wants to blow up.

if ( $(Try { Test-Path $MyPath.trim() } Catch { $false }) ) {  #Returns $false if $null, "" or " "
    write-host "path is GOOD"
} Else {
    write-host "path is BAD"
}

Evert · Accepted Answer · 2014-03-03 09:49:14Z

0

You should use Resolve-Path or Join-Path

answered Mar 3, 2014 at 9:49

Evert

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