5.15. Perl UNLESS…ELSE statement

One unless statement can be followed by an optional else statement else statement in a Boolean expression true when it is executed.

5.15.1. Grammar #

The syntax format is as follows:

unless(boolean_expression){ # In the Boolean expression boolean_ Expression executed with false }else{ # In the Boolean expression boolean_ Execute when expression is true } 

If a Boolean expression boolean_expression for false , then execute unless the code within the block. If the Boolean expression is true , then execute else the code within the block.

5.15.2. Flow chart #

5.15.3. Example #

Example #

#/ Usr/bin/perl $a=100# Using the 'less' statement to detect the Boolean expression' less' ($a==20){# When the Boolean expression is false, execute printf "Given condition is false n";} Else{# Execute printf when Boolean expression is true "Given condition is true 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 "a given condition is false n";} Else {# Boolean expression is true When executing printf "a, the given condition is true n";} The value of print "a is: $a n"; 

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

The given condition is false The value of a is: 100 The condition given by a is false The value of a is: 