5.16. Perl UNLESS…ELSIF statement

One unless statement can be followed by an optional elsif statement, and then follow another else statement.

This conditional judgment statement is very useful in the case of multiple conditions.

You need to pay attention to the following points when using the unless , elsif , and else statements.

• unless statement can be followed by 0 or 1 else statement, but elsif must be in the back else statement.

• unless statement can be followed by 0 or 1 elsif statements, but they must be written in the else before the statement.

• If one of them elsif successful execution, others elsif and else will no longer be executed.

unless(boolean_expression 1){ # In the Boolean expression boolean_ Expression 1 is executed as false } elsif( boolean_expression 2){ # In the Boolean expression boolean_ Expression 2 is executed as true } elsif( boolean_expression 3){ # In the Boolean expression boolean_ Expression 3 is executed as true } else{ # Execute when no conditions match } 

#/ Usr/bin/perl $a=20# Using the 'less' statement to detect the Boolean expression' less' ($a==30){# When the Boolean expression is false, execute printf 'a value is not 30 n';} Elsif ($a==30){# When the Boolean expression is true, execute printf "a with a value of 30 n";} Else{# When there is no condition matching, execute printf "the value of a is $a n";} 

The value of a is not 30