perl 回调必须是函数引用

[root@wx03 lib]# cat a1.pl 
use AE;
use AnyEvent;
##定义watch
my $t = AnyEvent->timer(
        after    => 0,
        interval => 5,
        cb       => sub {print test."\n";}
    );
    ##不要再每秒打印时间
    ##undef $t;
    my $cv = AnyEvent->condvar;
    $cv->recv;
[root@wx03 lib]# perl a1.pl 
test
test


[root@wx03 lib]# cat a1.pl 
use AE;
use AnyEvent;
##定义watch
my $t = AnyEvent->timer(
        after    => 0,
        interval => 5,
        cb       =>  print test."\n"
    );
    ##不要再每秒打印时间
    ##undef $t;
    my $cv = AnyEvent->condvar;
    $cv->recv;
[root@wx03 lib]# perl a1.pl 
test
1: callback must be a CODE reference or another callable object at /usr/local/perl/lib/site_perl/5.22.1/x86_64-linux/AnyEvent/Impl/EV.pm line 50.

回调必须是一个函数引用或者而另外的回调对象