Variable within a DOS command

[TuMiM]

Is it possible to put a variable into a DOS command within a script? I am trying to do this but it failes every time. What am I doing wrong or is it not possible?

$date = _NowDate()

RunWait(@ComSpec & " /c " & 'xcopy c:\temp\a\*.* c:\temp\b /S/E/Y/D:$date>c:\STLCopy.txt',"c:\", @SW_HIDE)

[Jos]

RunWait(@ComSpec & " /c " & 'xcopy c:\temp\a\*.* c:\temp\b /S/E/Y/D:' & $date & '>c:\STLCopy.txt',"c:\", @SW_HIDE)