Perl 条件判断语句

if 系列语句有一下几种：

if语句语法：

if ( some_expression ){
	true_statement1;
	true_statement2;
	...
}
next_statment;

if else 语句语法:

if ( some_expression ){
	true_statement1;
	true_statement2;
	...
}
else{
	false_statement1;
	false_statement2;
	....
}
next_statment;
...

if ( some_expression_one ){
	one_true_statement1;
	one_true_statement2;
}
elsif ( some_expression_two )｛
	two_true_statement1;
	two_true_statement2;
｝
elsif ( some_expression_three ){
	three_true_statement1;
	three_true_statement2;
}
else{
	all_false_statement1;
	all_false_statement2;
}
next_statment;
...

#!/usr/bin/perl
 
$number=<>;
chomp($number);
if($number > 0){
	print ("pulsn");
}
else{
	if ($number < 0){
		print ("minusn");
	}
	else{
		print ("zeron");
	}
}

unless语法：

unless(some_expression){
	false_statement1;
	false_statement2;
}

unless( some_expression){
	false_statement1;
	false_statement2;
}
else{
	true_statement1;
	true_statement2;
}

#!/usr/bin/perl   
  
$number=<>;
chomp($number);
unless($number != 0){
	print ("zeron");
}
else{
	unless ($number < 0){
		print ("plusn");
	}
	else{
		print ("minusn");
	}
}