【Perl读书笔记】defined函数

最新推荐文章于 2025-01-14 17:38:14 发布

原创最新推荐文章于 2025-01-14 17:38:14 发布 · 700 阅读

0 ·

CC 4.0 BY-SA版权

Perl 专栏收录该内容

14 篇文章

订阅专栏

本文通过一个Perl脚本示例，介绍了如何定义变量并检查其是否已定义。使用defined函数来判断变量是否存在，并展示了如何使变量变为未定义状态。

读《C程序员精通Perl》http://book.douban.com/subject/1232075/ 2.4.4节笔记

#!/usr/bin/perl
use strict;
use warnings;

my $name = "calf_man";
my $value;

if (defined($name)) {
        print "The name is defined as $name\n";
}

if (not defined($value)) {
        print "The value is not defined.\n";
}

#$name = undef; 
undef($name);
#undef #name;
if (not defined($name)) {
        print "The name is not defined.\n";
}

运行结果：

[root@localhost perl_practice]# ./define.pl
The name is defined as calf_man
The value is not defined.
The name is not defined.
[root@localhost perl_practice]#