NAME
  if - Execute scripts conditionally

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

DESCRIPTION
  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. 

EXAMPLE
  % set x 100
  100
  
  % if {$x > 50} {
      set y 200
    }
  200
  
  % if {$x < 40} {
      puts "x < 40"
    } elseif {$x >= 200} {
      puts "x >= 200"
    } elseif {$x == 100} {
      puts "x = 100"
    }
    x = 100

SEE ALSO
  case switch