envbackup.ps1

$ErrorActionPreference = 'Stop'

$timestamp_str = Get-Date -AsUTC -Format 'yyyy_MM_dd__HH_mm_ss'
$outdir = $PSScriptRoot

function backupregkeyhelper {
	[CmdletBinding(SupportsShouldProcess)]
	Param(
		[Parameter(Mandatory)]
		[string] $Path,
		[Parameter(Mandatory)]
		[string] $OutFileSlug
	)
	
	Process {
		$tempfile = New-TemporaryFile -WhatIf:$false -Confirm:$false
		$undated_outfile_hive = Join-Path $outdir "$OutFileSlug.hiv"
		$dated_outfile_hive   = Join-Path $outdir "$($OutFileSlug)__$timestamp_str.hiv"
		$undated_outfile_text = Join-Path $outdir "$OutFileSlug.reg"
		$dated_outfile_text   = Join-Path $outdir "$($OutFileSlug)__$timestamp_str.reg"
		try {
			# TODO check if reg ran successfully
			reg save   $Path $tempfile /y | Out-Null
			$new_hive = gc -AsByteStream -Raw -LiteralPath $tempfile
			reg export $Path $tempfile /y | Out-Null
			$new_text = gc -AsByteStream -Raw -LiteralPath $tempfile
			# get most recent data if any already saved
			$old_text = gc -AsByteStream -Raw -ErrorAction SilentlyContinue -LiteralPath $undated_outfile_text
			# we need to save the current data if a) there's no old data saved, or b) the data has changed
			$needs_save = ($old_text -eq $null) -or (@(Compare-Object -SyncWindow 0 $old_text $new_text).Length -gt 0)
			if($needs_save) {
				# TODO: doesn't properly handle -Confirm yes/no to all options
				#       https://learn.microsoft.com/en-us/powershell/scripting/learn/deep-dives/everything-about-shouldprocess
				Set-Content -LiteralPath $undated_outfile_hive -Value $new_hive -AsByteStream
				Set-Content -LiteralPath $dated_outfile_hive   -Value $new_hive -AsByteStream
				Set-Content -LiteralPath $undated_outfile_text -Value $new_text -AsByteStream
				Set-Content -LiteralPath $dated_outfile_text   -Value $new_text -AsByteStream
			}
		} finally {
			ri -WhatIf:$false -Confirm:$false -ErrorAction SilentlyContinue $tempfile
		}
	}
}


$regpath_machine_env = 'HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Environment'
$regpath_user_env    = 'HKCU\Environment'

backupregkeyhelper -Path $regpath_machine_env -OutFileSlug 'system_env'
backupregkeyhelper -Path $regpath_user_env    -OutFileSlug 'user_env'