          if test ?then? trueBody ?else? ?falseBody?
               The if command evaluates test as an expression (in  the
               same  way that expr evaluates its argument).  The value
               of the expression must be numeric; if  it  is  non-zero
               then  trueBody  is  called  by  passing  it  to the Tcl
               interpreter.   Otherwise  falseBody  is   executed   by
               passing  it  to the Tcl interpreter.  The then and else
               arguments are optional  ``noise  words''  to  make  the
               command easier to read.  FalseBody is also optional; if
               it isn't specified then the  command  does  nothing  if
               test  evaluates  to  zero.  The return value from if is
               the value of the last command executed in  trueBody  or
               falseBody,  or  the  empty  string if test evaluates to
               zero and falseBody isn't specified.
