October 2022
Beginner to intermediate
390 pages
7h 5m
Chinese
Content preview from Perl语言入门（第8版）
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进程管理
｜
273
而
system
的返回值是一个高低各
8
位的字节。“高”
8
位是程序的退出值，可以通过
第
12
章介绍的位操作符将它移低
8
位后取得：
my $return_value = system( ... );
my $child_exit_code = $return_value >> 8;
“低”
8
位包含了很多信息，其中最高的一位表示程序运行时是否发生了核心转储
（
core dump
）。利用十六进制数和二进制数（回想下第
12
章讲的内容）可以屏蔽掉
你不感兴趣的位：
my $low_octet = $return_value & 0xFF; #
屏蔽过滤掉高
8
位
my $dumped_core = $low_octet & 0b1_0000000; #
或写成
128
my $signal_number = $low_octet & 0b0111_1111; #
或写成
0x7f
或
127
由于
Windows
没有通知进程的信号机制，所以返回值各个位上的意义会有所不同。
可能你的系统会设置特定的错误消息到特殊变量
$^E
或
${^CHILD_ERROR_
NATIVE}
。参阅
perlrun
文档以及
POSIX
模块的文档（特别是有关
W*
宏的部
分，看看如何解构信号的意义）。
环境变量
在用这里讨论的方法启动外部进程时，可能会需要设置程序的环境。前面谈到我们可
以在一个特定的工作目录下启动进程，然后它会从父进程继承这个工作目录。所以我
们可以通过设置好环境变量，使外部进程按此工作。 ...
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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.