Powershell UNC Path not supported exception

Question

Well I've struggled long enough with this one. I have a project to compare two folders, one on each of two servers. We are comparing files on the source server with those on the target server and will create a list of the files from the source that will need to be refreshed once an update is completed on the target server.

Here's my script (many thanks to http://quickanddirtyscripting.wordpress.com for the original) :

param ([string] $src,[string] $dst)

function get-DirHash()
{
    begin 
    {
        $ErrorActionPreference = "silentlycontinue"
    }
    process 
    {
        dir -Recurse $_ | where { $_.PsIsContainer -eq $false -and ($_.Name -like "*.js" -or $_.Name -like "*.css"} | select Name,FullName,@{Name="SHA1 Hash"; Expression={get-hash $_.FullName -algorithm "sha1" }}
    }
    end 
    {
    }
}  

function get-hash 
{
    param([string] $file = $(throw 'a filename is required'),[string] $algorithm = 'sha256')
    try
    {
        $fileStream = [system.io.file]::openread((resolve-path $file));
        $hasher = [System.Security.Cryptography.HashAlgorithm]::create($algorithm);
        $hash = $hasher.ComputeHash($fileStream);
        $fileStream.Close();
    }
    catch
    {
        write-host $_
    }
    return $hash
}

Compare-Object $($src | get-DirHash) $($dst | get-DirHash) -property @("Name", "SHA1 Hash")

Now for some reason if I run this against local paths say c:\temp\test1 c:\temp\test2 it works fine, but when I run it using UNC paths between two servers I get

Exception calling "OpenRead" with "1" argument(s): "The given path's format is not supported."

Any help with this would be greatly appreciated. The end result should be a list of files, but for some reason it doesn't like the UNC path.

The script name is compare_js_css.ps1 and is called as such:

.\compare_js_css.ps1 c:\temp\test1 c:\temp\test2 <-- This works

.\compare_js_css.ps1 \\\\devserver1\c$\websites\site1\website \\\\devserver2\c$\websites\site1\website <-- Returns the aforementioned exception.

Why?

Answer 1

This gives the path you are after without the Microsoft.PowerShell.Core\FileSystem:::

(Resolve-Path $file).ProviderPath

No need to use a string replace.

Answer 2

OpenRead supports UNC paths. Resolve-Path returns you an object. Use (Resolve-Path MyFile.txt).Path.Replace('Microsoft.PowerShell.Core\FileSystem::', '') as the argument for OpenRead. The path returned from Resolve-Path when using UNC paths includes PowerShell's fully qualified schema which contains a header which is unsupported by the OpenRead method so it needs to be omitted.