5.14. Perl UNLESS statement

One unless statement consists of a Boolean expression followed by oneor more statements.

5.14.1. Grammar #

The syntax format is as follows:

unless(boolean_expression){
   # In the Boolean expression boolean_ Expression executed with false
}

If a Boolean expression boolean_expression for false , then if block of code within the statement will be executed. If the Boolean expression is true , then if the first set of code at the end of the statement (after closing parentheses) is executed.

5.14.2. Flow chart #

Example #

#/ Usr/bin/perl $a=20# Using the 'less' statement to detect the Boolean expression' less' ($a<20){#
When the Boolean expression is false, execute printf "a is greater than or equal to 20 n";} The value of print 'a' is
: $a n "; $a=" "; # Use the less statement to detect the Boolean expression less ($a) {# The Boolean expression is
When false, execute printf 'condition a is false n';} The value of print "a is: $a n";

Execute the above program, and the output is as follows:

A greater than or equal to 20
The value of a is: 20
Condition a is false
The value of a is: