if(n)                        Tcl Built-In Commands                       if(n)


       if - Execute scripts conditionally

       if expr1 ?then? body1 elseif expr2 ?then? body2 elseif ... ?else?

       The if command evaluates expr1 as an expression (in the same way that
       expr evaluates its argument).  The value of the expression must be a
       boolean (a numeric value, where 0 is false and anything is true, or a
       string value such as true or yes for true and false or no for false);
       if it is true then body1 is executed by passing it to the Tcl
       interpreter.  Otherwise expr2 is evaluated as an expression and if it
       is true then body2 is executed, and so on.  If none of the expressions
       evaluates to true then bodyN is executed.  The then and else arguments
       are optional ``noise words'' to make the command easier to read.  There
       may be any number of elseif clauses, including zero.  BodyN may also be
       omitted as long as else is omitted too.  The return value from the
       command is the result of the body script that was executed, or an empty
       string if none of the expressions was non-zero and there was no bodyN.

       boolean, conditional, else, false, if, true

Tcl                                                                      if(n)