Separate files into those used for setup and those used at runtime.

Files used for both will go in the run tree.

setup/windows/setup-piForHeadlessConfig.ps1

@@ -0,0 +1,61 @@
+[CmdletBinding()]
+Param
+(
+    [Parameter(Mandatory=$True,Position=1)]
+    [string]$driveLetter,
+	
+    [Parameter(Mandatory=$True,Position=2)]
+    [string]$wifiSSID,
+
+    [Parameter(Mandatory=$True,Position=3)]
+    [string]$wifiPSK
+)
+
+$drivePath="${driveLetter}:"
+$configPath = "$drivePath\config.txt"
+$cmdlinePath = "$drivePath\cmdline.txt"
+$sshPath = "$drivePath\ssh"
+
+if ((![System.IO.File]::Exists($configPath) -or
+    (![System.IO.File]::Exists($cmdlinePath)))) {
+    Write-Error "Didn't find cmdline.txt and config.txt on drive $drivePath."
+    exit 1
+}
+
+Write-Verbose "Updating $configPath ..."
+
+"" | Out-File -FilePath $configPath -Append -Encoding utf8
+"dtoverlay=dwc2" | Out-File -FilePath $configPath -Append -Encoding utf8
+
+Write-Verbose "Updating $cmdlinePath ..."
+$cmdlinetxtContent = gc -Raw $cmdlinePath
+$cmdlinetxtContent.Replace("rootwait", "rootwait modules-load=dwc2,g_ether").Replace(" init=/usr/lib/raspi-config/init_resize.sh", "") | Out-File -FilePath $cmdlinePath -Encoding utf8
+
+Write-Verbose "Enabling SSH ..."
+[System.IO.File]::CreateText($sshPath).Dispose()
+
+# Sets up wifi credentials so wifi will be 
+# auto configured on first boot
+
+$wpaSupplicantConfPath="$drivePath\wpa_supplicant.conf"
+
+Write-Verbose "(Re)creating WiFi configuration file $wpaSupplicantConfPath."
+if ([System.IO.File]::Exists("$wpaSupplicantConfPath")) {
+  del "$wpaSupplicantConfPath"
+}
+
+$wpaSupplicantConfContent=@"
+ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
+update_config=1
+
+network={
+  ssid="$wifiSSID"
+  psk="$wifiPSK"
+}
+"@
+
+$utf8 = New-Object System.Text.UTF8Encoding $false
+
+Set-Content -Value $utf8.GetBytes($wpaSupplicantConfContent) -Encoding Byte -Path "$wpaSupplicantConfPath"
+
+Write-Verbose "All done."

setup/windows/setup-piForHeadlessConfigAddWifi.ps1

@@ -0,0 +1,31 @@
+[CmdletBinding()]
+Param
+(
+    [Parameter(Mandatory=$True,Position=1)]
+    [string]$driveLetter,
+	
+    [Parameter(Mandatory=$True,Position=2)]
+    [string]$wifiSSID,
+
+    [Parameter(Mandatory=$True,Position=3)]
+    [string]$wifiPSK
+)
+
+$drivePath="${driveLetter}:"
+
+$wpaSupplicantConfPath="$drivePath\wpa_supplicant.conf"
+
+$wpaSupplicantConfContent=@"
+
+
+network={
+  ssid="$wifiSSID"
+  psk="$wifiPSK"
+}
+"@
+
+$utf8 = New-Object System.Text.UTF8Encoding $false
+
+Add-Content -Value $utf8.GetBytes($wpaSupplicantConfContent) -Encoding Byte -Path "$wpaSupplicantConfPath"
+
+Write-Verbose "All done."