Script to set "Hide file extensions"

You need to create two .reg files.

To hide extensions

reg add HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced /v HideFileExt /t REG_DWORD /d 1 /f

To show extensions

reg add HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced /v HideFileExt /t REG_DWORD /d 0 /f

Here is a Powershell version

function ShowFileExtensions() 
{
    Push-Location
    Set-Location HKCU:\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    Set-ItemProperty . HideFileExt "0"
    Pop-Location
}

function HideFileExtensions() 
{
    Push-Location
    Set-Location HKCU:\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    Set-ItemProperty . HideFileExt "1"
    Pop-Location
}

I found this autohotkey solution at: How to write an autohotkey script to toggle the Show hidden files and folders setting?

This is especially nice because it also handles refreshing the explorer to make the change visible.

;------------------------------------------------------------------------
; Show hidden folders and files in Windows XP
;------------------------------------------------------------------------
; User Key: [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced]
; Value Name: Hidden
; Data Type: REG_DWORD (DWORD Value)
; Value Data: (1 = show hidden, 2 = do not show)

    #h::

        RegRead, ShowHidden_Status, HKEY_CURRENT_USER, Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced, Hidden
        if ShowHidden_Status = 2 
        RegWrite, REG_DWORD, HKEY_CURRENT_USER, Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced, Hidden, 1
        Else
        RegWrite, REG_DWORD, HKEY_CURRENT_USER, Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced, Hidden, 2
        WinGetClass, CabinetWClass
        PostMessage, 0x111, 28931,,, A
        Return