Invoke-WinMerge.ps1

function Invoke-WinMerge {
    <#
        .SYNOPSIS
            Wrapper for WinMerge.
        .DESCRIPTION
            PowerShell wrapper for WinMerge. Let's you launch file/folder comparison using WinMerge
            from the PowerShell console.
        .EXAMPLE
            Invoke-WinMerge c:\temp\file1.txt c:\temp\file2.txt
            Will launch WinMerge to compare file1.txt and file2.txt.
        .EXAMPLE
            .EXAMPLE
            Invoke-WinMerge c:\folder1 c:\folder2
            Will launch WinMerge to compare folder1 and folder2.
        .NOTES
            Author: Øyvind Kallstad
            Date: 17.01.2016
            Version: 1.1
        .LINK
            https://communary.wordpress.com/
    #>
    [CmdletBinding()]
    param (
        # Specifies the folder, file, or project file to open on the left side.
        [Parameter(Position = 1, Mandatory = $true)]
        [ValidateNotNullOrEmpty()]
        [string] $LeftPath,

        # Specifies the folder, file, or project file to open on the right side.
        [Parameter(Position = 2, Mandatory = $true)]
        [ValidateNotNullOrEmpty()]
        [string] $RightPath,

        # Path to WinMergeU.exe. If not specified, the function will try to locate
        # the path from the Windows Registry.
        [Parameter()]
        [string] $PathToWinMergeU = $null,

        # Applies a specified filter to restrict the comparison. 
        # The filter can be a filemask like *.h *.cpp, or the name of a file filter like XML/HTML Devel. 
        # Add quotation marks around a filter mask or name that contains spaces.
        [Parameter()]
        [string] $Filter,

        # Compares all files in all subfolders (recursive compare). 
        # Unique folders (occurring only on one side) are listed in the compare result as separate items. 
        # Note that including subfolders can increase compare time significantly. 
        # Without this parameter, WinMerge lists only files and subfolders at the top level of the two target folders. It does not compare the subfolders.
        [Parameter()]
        [switch] $Recurse,

        # Closes WinMerge when you start a comparison of identical files. It will not work when comparing folders.
        # The parameter has no effect after the comparison, for example if the files become identical as a result of merging or editing. 
        [Parameter()]
        [switch] $CloseOnSame
    )

    $regPath1 = 'HKCU:\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\WinMergeU.exe'
    $regPath2 = 'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\WinMergeU.exe'
    $notFoundMessage = 'WinMergeU.exe not found! You can download WinMerge from http://winmerge.org/'

    # if no path to WinMergeU.exe is given by the user, try to get it from the registry
    if (-not $PathToWinMergeU) {
        if (Test-Path -Path $regPath1) {
            $exePath = Get-ItemProperty $regPath1 | Select-Object -ExpandProperty '(default)'
        }
        elseif (Test-Path -Path $regPath2) {
            $exePath = Get-ItemProperty $regPath2 | Select-Object -ExpandProperty '(default)'
        }
        else {
            Write-Warning $notFoundMessage
            break
        }
    }

    else {
        $exePath = $PathToWinMergeU
    }
    

    if (Test-Path -Path $exePath) {
        
        $leftExist = Test-Path -Path $LeftPath
        $rightExist = Test-Path -Path $RightPath

        if ($leftExist -and $rightExist) {
            if ((Get-Item -Path $LeftPath).FullName -eq (Get-Item -Path $RightPath).FullName) {
                Write-Warning 'Left and Right paths are the same. Did you mean to do that?'
                break
            }

            $parameters = New-Object System.Collections.ArrayList

            # /e enables you to close WinMerge with a single Esc key press. 
            # This is useful when you use WinMerge as an external compare application: you can close WinMerge quickly, like a dialog. 
            # Without this parameter, you might have to press Esc multiple times to close all its windows. 
            [void]$parameters.Add('/e')

            # /u prevents WinMerge from adding either path (left or right) to the Most Recently Used (MRU) list. 
            # External applications should not add paths to the MRU list in the Select Files or Folders dialog. 
            [void]$parameters.Add('/u')

            if ($CloseOnSame) {
                [void]$parameters.Add('/xq')
            }

            if ($Recurse) {
                [void]$parameters.Add('/r')
            }

            if ($Filter) {
                [void]$parameters.Add('/f')
                [void]$parameters.Add("`"$Filter`"")
            }

            [void]$parameters.Add("`"$LeftPath`"")
            [void]$parameters.Add("`"$RightPath`"")
        
            Start-Process -FilePath $exePath -ArgumentList $parameters
        }
        else {
            if (-not $leftExist) {
                Write-Warning "$($LeftPath) not found!"
            }
            if (-not $rightExist) {
                Write-Warning "$($RightPath) not found!"
            }
        }
    }

    else {
        Write-Warning $notFoundMessage
    }
}