Perl UNLESS statement

Author：Eve Cole Update Time：2024-12-24 10:48:01

An unless statement consists of a Boolean expression followed by one or more statements.

grammar

The syntax format is as follows:

 unless(boolean_expression){ # execute when boolean_expression is false}

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

flow chart

Example

#!/usr/bin/perl $a = 20 ; # Use the unless statement to detect Boolean expressions unless ( $a < 20 ) { #Executed when the Boolean expression is false printf " a is greater than or equal to 20 n " ; } print " The value of a is: $a n " ; $a = " " ; # Use the unless statement to detect Boolean expressions unless ( $a ) { #Executed when the Boolean expression is false printf " Condition a is false n " ; } print " The value of a is: $a n " ;

Executing the above program, the output result is:

 The value of a greater than or equal to 20a is: 20 The value of a if a is falsea is: