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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输入与输出
｜
111
使用文件句柄
文件句柄打开后，便可以像从
STDIN
读取标准输入流中的数据一样，一行行地读取它
的数据。来看读取
Unix
系统密码文件的例子：
if ( ! open PASSWD, "/etc/passwd") {
die "How did you get logged in? ($!)";
}
while (<PASSWD>) {
chomp;
...
}
这个例子里，
die
发出的消息中用了一对括号围住
$!
。不要误会，这里的括号是要让
系统错误的原因更清楚，有时候标点符号就只是标点符号。来看第二部分，我们之前
所说的行输入操作符其实是由两部分组成的：一对尖括号（也就是真正的行输入操作
符）以及要读取数据的文件句柄。
打开的文件句柄可以通过
print
或
printf
写入或追加数据。使用时将文件句柄直接
跟在函数名之后、参数列表之前即可：
print LOG "Captain's log, stardate 3.14159\n"; #
输出到文件句柄
LOG
printf STDERR "%d percent complete.\n", $done/$total * 100;
注意，文件句柄和要输出的内容之间没有逗号。这里如果加上括号的话看起来会更古
怪，所以习惯上直接省略。非要加上的话，下面两种写法都是正确的：
printf (STDERR "%d percent complete.\n", $done/$total * 100);
printf STDERR ("%d ...
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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.