August 2018
Beginner to intermediate
382 pages
7h 14m
Chinese
Content preview from Perl语言入门
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输入与输出
｜
109
用
warn
发出警告信息
类似
die
函数能提示
Perl
的内置错误这样的致命错误（比如除以零），
warn
函数
可以发出类似于
Perl
的内置警告信息这样的信息（比如启用警告信息时，使用某
个
undef
变量参与运算就会发出警告信息）。
warn
函数的功能和
die
差不多，不同之处仅在最后一步：它不会终止程序的运行。
其他都不变，如有需要它也会提供出错的程序名及行号，同样会将错误信息送往标准
错误流。
自动检测致命错误
从
Perl 5.10
开始，
autodie
编译指令已成为标准库的一部分。比如下面这个例子，之
前的写法是自己检查
open
操作是否成功：
if ( ! open LOG, '>>', 'logfile' ) {
die "Cannot create logfile: $!";
}
每次打开文件句柄都要这么写的话，确实够麻烦的。现在开始用
autodie
编译指令，
它会在
open
失败时自动启动
die
：
use autodie;
open LOG, '>>', 'logfile';
这条编译指令会识别
Perl
内置函数是否调用操作系统接口，这种调用时出现的错误
并非程序员所能控制的，所以一旦发现，
autodie
便会自动帮你调用
die
发出错误信
息，信息的内容大体和我们自己组织的差不多：
Can't open('>>', 'logfile'): No such file or directory at test line 3
我们已经介绍了出现错误时的处理，现在回到 ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.