如何在strict pragma下将变量设置为NULL？

Question

use strict;
my $var = NULL;

会引起错误 Bareword "NULL" not allowed while "strict subs" in use

Answer 1

Perl中没有NULL.但是,变量可以被undef定义,这意味着它们没有设置值.
以下是一些如何在Perl中获取未定义变量的示例:

my $var;       # variables are undefined by default
undef $var;    # undef() undefines the value of a variable
$var = undef;  # same, using an alternative syntax

要检查变量的定义,请使用defined(),即

print "\$var is undefined\n" unless defined $var;