From Valve Developer Community
Note:Variables do not work within "quote blocks"!
Note:Variables do not work within macros either. You can pass the data on to the macro by using it as a token when running it.
Note:If you define the same variable twice, the compiler will use the first one it finds and drop the second one.
This command is a 'lite' version of $definemacro.
$definevariable baseFile "fighter1" $sequence attack $baseFile$_Attack $sequence run $baseFile$_Run $sequence idle $baseFile$_Idle