Perl 中的 unless...elsif..else 语句

除非unless语句后可以跟可选的 elsif ... else 语句，这对于使用单个unless... elsif语句测试各种条件非常有用。

unless...elsif..else - 语法

Perl编程语言中的unless...elsif ... else 语句的语法是-

unless(boolean_expression 1) {
   # Executes when the boolean expression 1 is false
} elsif( boolean_expression 2) {
   # Executes when the boolean expression 2 is true
} elsif( boolean_expression 3) {
   # Executes when the boolean expression 3 is true
} else {
   # Executes when the none of the above condition is met
}

unless...elsif..else - 示例

#!/usr/local/bin/perl
 
$a=20;
# check the boolean condition using if statement
unless( $a  ==  30 ) {
   # if condition is false then print the following
   printf "a has a value which is not 20\n";
} elsif( $a ==  30 ) {
   # if condition is true then print the following
   printf "a has a value which is 30\n";
} else {
   # if none of the above conditions is met
   printf "a has a value which is $a\n";
}

在这里，我们使用等于运算符==，用于检查两个操作数是否相等。如果两个操作数相同，则返回true，否则重新运行为false。

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a has a value which is not 20