A Sitecore PowerShell Extensions script for comparison the fields of items.

compare-items.ps1

$resultTypes = [ordered]@{
    "Show all" = 1
    "Only matched" = 2
    "Only unmatched" = 4
}

function Get-ItemTitle {
    param (
        [Sitecore.Data.Items.Item]$Item
    )
    
    $displayName = $Item.DisplayName
    $databaseName = $Item.Database.Name
    $languageName = $Item.Language.Name
    $id = $Item.ID.Guid.ToString("D").SubString(0, 8)
    
    return "$displayName ($databaseName, $languageName, $id)"
}

function Get-Comparisons {
    param (
        [Sitecore.Data.Items.Item[]]$Items,
        [switch]$UseNameForFieldIdentifier
    )
    $fieldIdentifier = $(if ($UseNameForFieldIdentifier) {"Name"} else {"ID"})
    
    $fields = @()
    $Items | % { $_.Template.Fields | % { $fields += $_ } }
    $fields = $fields | Group-Object "$fieldIdentifier" | % { $_.Group | Select-Object -First 1 }

    $result = @()
    $fields | % {
        $field = $_
        $itemFields = $items | % { @{Title=$(Get-ItemTitle $_); FieldValue=$_[$field."$fieldIdentifier"]} }
        
        $row = [PSCustomObject]@{
            Matched = $($itemFields | % { $_.FieldValue } | Select-Object -Unique).Count -eq 1
            "Field Name" = $field.Name
        }
        $itemFields | % { $row | Add-Member $_.Title $_.FieldValue }
    
        $result += $row
    }
    
    return $result
}

function Show-ComparisonView {
    param (
        [Sitecore.Data.Items.Item[]]$Items,
        [Int]$ResultType,
        [switch]$IncludeStandardFields,
        [switch]$UseNameForFieldIdentifier
    )

    $iconProp = @{
        Name="Icon"
        Expression={
            if($_.Matched) {
                return "office/16x16/check.png"
            }
            else {
                return "office/16x16/delete.png"
            }
        }
    }    

    Get-Comparisons $Items -UseNameForFieldIdentifier:$UseNameForFieldIdentifier `
    | Where-Object { $(if ($IncludeStandardFields) { $true } else { -not $_."Field Name".StartsWith("__") }) } `
    | Where-Object { $(if ($ResultType -eq $resultTypes."Only matched") { $_.Matched } else { $true }) } `
    | Where-Object { $(if ($ResultType -eq $resultTypes."Only unmatched") { -not $_.Matched } else { $true }) } `
    | Select-Object *,$iconProp -ExcludeProperty Matched `
    | Show-ListView -Title "Item Comparison Result"    
}

$params = @(
    @{ Name = "items"; Title = "Select the items to compare"; Value = $SitecoreContextItem; Editor = "treelist"; Source="DatabaseName=$($SitecoreContextItem.Database.Name)&AllowMultipleSelection=no" },
    @{ Name = "resultType"; Title = "Select the result type"; Value = 1; Options=$resultTypes; Editor = "combo" },
    @{ Name = "includeStandardFields"; Title = "Include the standard fields"; Value = $false; Editor = "checkbox"; Columns = 6 },
    @{ Name = "useNameForFieldIdentifier"; Title = "Use the name for field identifier"; Value = $false; Editor = "checkbox"; Columns = 6 }
)
$result = Read-Variable -Parameters $params -Title "Item Comparison Settings" -Description "Set the items and the options for comparison."

if ($result -ne "ok") {
    Exit
}

if ($items.Length -lt 2) {
    Show-Alert "Select two or more items to compare."
    Exit
}

Show-ComparisonView $items $resultType -IncludeStandardFields:$includeStandardFields -UseNameForFieldIdentifier:$useNameForFieldIdentifier