07-15-2015
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man bash:
Quote:
for (( expr1 ; expr2 ; expr3 )) ; do list ; done
First, the arithmetic expression expr1 is evaluated according to the rules described below under ARITHMETIC EVALUATION. The arithmetic expression expr2 is then evaluated repeatedly until it evaluates to zero. Each time expr2 evaluates to a non-zero value, list is executed and the arithmetic expression expr3 is evaluated. If any expression is omitted, it behaves as if it evaluates to 1. The return value is the exit status of the last command in list that is executed, or false if any of the expressions is invalid.
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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 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(n), for(n), foreach(n)
KEYWORDS
boolean, conditional, else, false, if, true
Tcl if(n)