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if(3tcl)


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.

EXAMPLES

   A simple conditional:
          if {$vbl == 1} { puts "vbl is one" }

   With an else-clause:
          if {$vbl == 1} {
             puts "vbl is one"
          } else {
             puts "vbl is not one"
          }

   With an elseif-clause too:
          if {$vbl == 1} {
             puts "vbl is one"
          } elseif {$vbl == 2} {
             puts "vbl is two"
          } else {
             puts "vbl is not one or two"
          }

   Remember, expressions can be multi-line, but in that case it can  be  a
   good idea to use the optional then keyword for clarity:
          if {
             $vbl == 1 || $vbl == 2 || $vbl == 3
          } then {
             puts "vbl is one, two or three"
          }

SEE ALSO

   expr(3tcl), for(3tcl), foreach(3tcl)

KEYWORDS

   boolean, conditional, else, false, if, true



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