Get filename in the case stored on disk?

Here's what I came up with:

function Get-ActualFileName($file) {
    $parent = Split-Path $file
    $leaf = Split-Path -Leaf $file

    $result = Get-ChildItem $parent | where { $_ -like $leaf }
    $result.Name
}

The following PowerShell function is based on another developer's elegant solution for C# at https://stackoverflow.com/a/11436327/854680.

Because Get-ChildItem is not used, it is much faster, which makes a difference when calling this function dozens or hundreds of times.

function Get-FileNameTrueCase {
    Param (
        [parameter(Mandatory=$true)]
        [string]
        $DirOrFile
    )

    if (-not ( (Test-Path $DirOrFile -PathType Leaf) -or (Test-Path $DirOrFile -PathType Container) ) ) {
        # File or directory not found
        return $DirOrFile
    }

    $TruePath = "";
    foreach ($PathPart in $DirOrFile.Split("\")) {
        if ($TruePath -eq "") {
            $TruePath = $PathPart.ToUpper() + "\";
            continue;
        }
        $TruePath = [System.IO.Directory]::GetFileSystemEntries($TruePath, $PathPart)[0];
    }
    return $TruePath;
}

Rather than specifying the exact name, just use a wildcard:

PS> Get-Item ReadMe.tx?

this should return README.TXT