The difference between the two looping statements is as follows:

• in a do-while statement the block is repeatedly executed as long as the condition is true
• a do-until statement is repeatedly executed as long as the test condition remains false

The main syntax form of the Perl do-until statement is as follows:

do BLOCK until (EXPR);

The following script examples show you a few ways about how to use the Perl do-until statements in your Perl script applications.


Example 1.

The next example will read a command word from the standard input and it will end the loop when you’ll input the word "stop". As you see Perl continues to iterate the loop as long as the condition that follows the block remains false (i.e. the input command is not "stop").

my $command;
do {
  # ask for the input command 
  print "Command: ";       
  # get the input from STDIN and 
  # chomp off the trailing newline
  chomp($command = <STDIN>);  
  # convert $command to lowercase
  lc($command);
  # convert the first character in uppercase
  $command = ucfirst $command;
}
until($command eq "Stop");

This code snippet is shown in conjunction with the arrays and hashes. It will calculate the total amount of birds which can be found in a particular household.

# initialize a hash (associative array)
%birds = (hen => 12, ducks => 15, geese => 5);
# put the bird names in an array
@birdNames = keys(%birds);

# initialize a count scalar variable
$count = 0;
do {
  # get the first element of the array
  $name = shift(@birdNames);
  # add to count the number of the current bird
  $count += $birds{$name};
} until (!@birdNames);

# displays the total amount of birds
print "Total: $count\n";
# displays Total: 32