Coming from an Oracle background, Oracle\'s SQLPlus would let you indicate a variable. If the variable wasn\'t set, you\'d be prompted to provide a value.
SQLCMD does not support prompting for missing variable names. However, you can use SSMS in SQLCMD mode. Dunno how you're error was caused, but this works for me:
:setvar table "sys.tables"
SELECT * FROM $(table);