Wednesday, 9 April 2014

unless-else statement



Perl UNLESS...ELSE statement

A Perl unless statement can be followed by an optional else statement, which executes when the boolean expression is true.

Syntax:

The syntax of an unless...else statement in Perl programming language is:
unless(boolean_expression){
   # statement(s) will execute if the given condition is false
}else{
   # statement(s) will execute if the given condition is true
}
If the boolean expression evaluates to true then the unless block of code will be executed otherwise else block of code will be executed.

Example:

#!/usr/local/bin/perl
 
$a = 100;
# check the boolean condition using unless statement
unless( $a == 20 ){
    # if condition is false then print the following
    printf "given condition is false\n";
}else{ 
    # if condition is true then print the following
    printf "given condition is true\n";
}
print "value of a is : $a\n";
 
$a = "";
# check the boolean condition using unless statement
unless( $a ){
    # if condition is false then print the following
    printf "a has a false value\n";
}else{
   # if condition is true then print the following
    printf "a has a true value\n";
}
print "value of a is : $a\n";
 
When the above code is executed, it produces following result:
given condition is false
value of a is : 100
a has a false value
value of a is : 

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