if(n) Tcl Built-In Commands if(n)
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 inter-
preter. 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 to make the command easier to read. There may be any num-
ber 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
if(n), if(n), if(n)
KEYWORDS
boolean, conditional, else, false, if, true
Tcl if(n)
tcl 8.6.0 - Generated Wed Jan 9 15:02:11 CST 2013