When working with Windows environment variables across different architectures, developers often encounter surprising inconsistencies. The %ProgramFiles% variable demonstrates particularly interesting behavior:

:: Command Prompt behavior
> echo %ProgramFiles%
C:\Program Files

:: PHP behavior
> php -r "echo $_ENV['ProgramFiles'];"
C:\Program Files (x86)

This discrepancy stems from Windows' WOW64 (Windows 32-bit on Windows 64-bit) subsystem. When 32-bit applications run on 64-bit Windows, the system automatically redirects certain file system and registry paths:

:: Native 64-bit process sees
%ProgramFiles% → C:\Program Files
%ProgramFiles(x86)% → C:\Program Files (x86)

:: 32-bit process sees
%ProgramFiles% → C:\Program Files (x86)
%ProgramFiles(x86)% → C:\Program Files (x86)

For cross-platform scripts, consider these approaches:

:: Batch file solution
@echo off
IF EXIST "%SystemRoot%\SysWOW64" (
    set "PROGFILES=%ProgramFiles%"
) ELSE (
    set "PROGFILES=%ProgramFiles(x86)%"
)

:: PowerShell alternative
$programFiles = if ([Environment]::Is64BitOperatingSystem) {
    ${env:ProgramFiles}
} else {
    ${env:ProgramFiles(x86)}
}

:: C# implementation
string programFiles = Environment.GetFolderPath(
    Environment.Is64BitProcess ? 
    Environment.SpecialFolder.ProgramFiles : 
    Environment.SpecialFolder.ProgramFilesX86);

• Use %ProgramFiles% when your application matches the OS architecture
• Use %ProgramFiles(x86)% explicitly for 32-bit applications
• For mixed scenarios, implement architecture detection logic

Note that similar redirection occurs in the registry. The HKLM\Software key redirects to HKLM\Software\WOW6432Node for 32-bit applications. Always specify KEY_WOW64_64KEY or KEY_WOW64_32KEY flags when accessing registry programmatically.

When working with Windows environment variables, particularly %ProgramFiles%, developers often encounter inconsistencies between different execution contexts. The behavior changes depending on whether the process is running as 32-bit or 64-bit on a 64-bit Windows system.

Here's what happens in different scenarios:

// From 64-bit command prompt:
C:\> echo %ProgramFiles%
C:\Program Files

// From 32-bit application (like 32-bit PHP):
php -r "echo $_ENV['ProgramFiles'];"
C:\Program Files (x86)

The difference occurs because of Windows' File System Redirector, which transparently redirects file operations for 32-bit applications:

• For 64-bit processes: %ProgramFiles% points to C:\Program Files
• For 32-bit processes: %ProgramFiles% points to C:\Program Files (x86)

Here are several approaches to handle this in your code:

// Method 1: Using WOW64 redirection awareness (C# example)
[DllImport("kernel32.dll", SetLastError = true)]
static extern bool Wow64DisableWow64FsRedirection(ref IntPtr ptr);

public static string GetTrueProgramFilesPath()
{
    IntPtr wow64Value = IntPtr.Zero;
    bool disabled = Wow64DisableWow64FsRedirection(ref wow64Value);
    string path = Environment.GetEnvironmentVariable("ProgramFiles");
    if (disabled) Wow64RevertWow64FsRedirection(wow64Value);
    return path;
}

Or a simpler PowerShell approach:

# PowerShell method
$trueProgramFiles = [Environment]::GetEnvironmentVariable("ProgramFiles", "Machine")
if ([Environment]::Is64BitProcess -and ![Environment]::Is64BitOperatingSystem) {
    $trueProgramFiles = $trueProgramFiles -replace " $x86$$", ""
}

Windows provides additional variables that might be useful:

%ProgramFiles%        = Current architecture view
%ProgramW6432%       = Always 64-bit Program Files (on 64-bit Windows)
%ProgramFiles(x86)%  = Always 32-bit Program Files

For batch scripts that need to work in both environments:

@echo off
:: Detect true Program Files location
if exist "%ProgramW6432%" (
    set TRUE_PROGRAM_FILES=%ProgramW6432%
) else (
    set TRUE_PROGRAM_FILES=%ProgramFiles%
)

echo True Program Files location: %TRUE_PROGRAM_FILES%