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.
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.
Flow chart
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: