until loop in perl-IGI

The until loop in Perl is similar to the while loop, but with the condition inverted. The loop continues executing until the condition evaluates to true. The syntax of the until loop is as follows:

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until (condition) {
    # code to be executed
}

In this syntax, the condition is a Boolean expression that is evaluated before each iteration of the loop. If the condition evaluates to false, the code block is executed. If the condition evaluates to true, the loop terminates and control is passed to the next statement after the loop.

Here's an example of an until loop that counts down from 10 to 1 and prints each number:

my $countdown = 10;
until ($countdown == 0) {
    print "$countdown\n";
    $countdown--;
}

In this example, the until loop continues executing until $countdown is equal to 0. During each iteration of the loop, the current value of $countdown is printed, and then it is decremented by 1 using the $countdown-- statement. When $countdown is equal to 0, the loop terminates and control is passed to the next statement after the loop.

You can also use the until loop to iterate over an array or a list, just like the while loop. Here's an example:

my @colors = qw(red green blue);
my $i = 0;
until ($i == scalar @colors) {
    print "$colors[$i]\n";
    $i++;
}

In this example, the until loop iterates over the @colors array until $i is equal to the number of elements in the array, which is obtained using the scalar function. During each iteration of the loop, the current element of the array is printed using the $colors[$i] expression, and then $i is incremented by 1 using the $i++ statement. When $i is equal to the number of elements in the array, the loop terminates and control is passed to the next statement after the loop.

The until loop is useful when you want to execute a block of code until a certain condition is true, rather than while the condition is true.

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until loop in perl