In the following recipe, we will create a Tcl script, that accepts two numeric arguments (x and y), where y is greater than x, evaluates the existence of the arguments, and prints out the values between x and y.

Create a text file named nest.tcl that contains the following commands:

if {$argc == 2} {
	set x [lindex $argv 0]
	set y [lindex $argv 1]
	puts "Beginning the while loop"
	for {set i $x} {$i <= $y} {incr i} {puts $i}
} else {
	puts "Invalid number of arguments"
}

Now invoke the script using the following command line:

% tclsh85 nest.tcl 1
Invalid number of arguments

As you can see by the output, the if statement evaluated as false and the inner loop was never reached.

Now invoke the script using the following command line:

% tclsh85 nest.tcl 5 10
5
6
7
8
9
10

In this instance, we have entered the for loop and invoked the actions until our upper limit was reached.