Perl 除非语句后可以跟可选的 else 语句，该语句在布尔表达式为true时执行。

unless...else - 语法

Perl编程语言中的unless... else 语句的语法为-

unless(boolean_expression) {# statement(s) will execute if the given condition is false
} else {# statement(s) will execute if the given condition is true
}

如果布尔表达式的值为 true ，则将执行代码的除非块，否则将执行代码的 else块。

unless...else - 流程图

unless...else - 示例

#!/usr/local/bin/perl$a=100;
# check the boolean condition using unless statement
unless( $a == 20 ) {# if condition is false then print the followingprintf "given condition is false\n";
} else { # if condition is true then print the followingprintf "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 followingprintf "a has a false value\n";
} else {# if condition is true then print the followingprintf "a has a true value\n";
}
print "value of a is : $a\n";

执行以上代码后，将产生以下输出-

given condition is false
value of a is : 100
a has a false value
value of a is : 

Perl 中的 unless...else 语句函数 - 无涯教程网无涯教程网提供Perl 除非语句后可以跟可选的 else 语句，该语句在布尔表达式为true时执行。 unless.....https://www.learnfk.com/perl/perl-unless-else-statement.html