Perl 简明教程
Perl - Coding Standard
当然,每个程序员在格式方面的喜好不一样,但一些通用的准则会让你的程序更容易阅读、理解和维护。
Each programmer will, of course, have his or her own preferences in regards to formatting, but there are some general guidelines that will make your programs easier to read, understand, and maintain.
最重要的一件事是始终在 -w 标志下运行你的程序。如果必须,你可以通过 no warnings 规范或 $^W 变量明确针对特定代码段关闭它。你还应该始终在 use strict 下运行或知道为什么不用。use sigtrap 甚至 use diagnostics 规范可能也派得上用场。
The most important thing is to run your programs under the -w flag at all times. You may turn it off explicitly for particular portions of code via the no warnings pragma or the $^W variable if you must. You should also always run under use strict or know the reason why not. The use sigtrap and even use diagnostics pragmas may also prove useful.
关于代码布局的美学,Larry 强烈关注的唯一一件事是多行 BLOCK 的结束花括号应与启动构造的关键字对齐。除此之外,他还有一些不太强烈的偏好 -
Regarding aesthetics of code lay out, about the only thing Larry cares strongly about is that the closing curly bracket of a multi-line BLOCK should line up with the keyword that started the construct. Beyond that, he has other preferences that aren’t so strong −
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4-column indent.
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Opening curly on same line as keyword, if possible, otherwise line up.
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Space before the opening curly of a multi-line BLOCK.
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One-line BLOCK may be put on one line, including curlies.
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No space before the semicolon.
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Semicolon omitted in "short" one-line BLOCK.
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Space around most operators.
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Space around a "complex" subscript (inside brackets).
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Blank lines between chunks that do different things.
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Uncuddled elses.
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No space between function name and its opening parenthesis.
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Space after each comma.
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Long lines broken after an operator (except and and or).
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Space after last parenthesis matching on current line.
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Line up corresponding items vertically.
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Omit redundant punctuation as long as clarity doesn’t suffer.
下面列出一些其他更实质性的风格问题,供您思考:仅仅因为你能用某种特定的方式来做某件事,并不表示你应该用这种方式去做。Perl 的设计原则给予你多种方式来做任何事,所以考虑选择最具可读性的方式。例如 −
Here are some other more substantive style issues to think about: Just because you CAN do something a particular way doesn’t mean that you SHOULD do it that way. Perl is designed to give you several ways to do anything, so consider picking the most readable one. For instance −
open(FOO,$foo) || die "Can't open $foo: $!";
优于 −
Is better than −
die "Can't open $foo: $!" unless open(FOO,$foo);
因为第二种方式在修饰符中隐藏了语句的重点。另一方面,
Because the second way hides the main point of the statement in a modifier. On the other hand,
print "Starting analysis\n" if $verbose;
优于 −
Is better than −
$verbose && print "Starting analysis\n";
因为重点不是用户是否输入了 -v。
Because the main point isn’t whether the user typed -v or not.
不要执行愚蠢的扭曲操作,以便在顶部或底部退出一个循环,因为 Perl 提供了 last 操作符,让你可以在循环中退出。只需对它进行一点“缩进”使它更明显 −
Don’t go through silly contortions to exit a loop at the top or the bottom, when Perl provides the last operator so you can exit in the middle. Just "outdent" it a little to make it more visible −
LINE:
for (;;) {
statements;
last LINE if $foo;
next LINE if /^#/;
statements;
}
让我们看一看其他几个重要要点 −
Let’s see few more important points −
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Don’t be afraid to use loop labels—they’re there to enhance readability as well as to allow multilevel loop breaks. See the previous example.
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Avoid using grep() (or map()) or
backticks
in a void context, that is, when you just throw away their return values. Those functions all have return values, so use them. Otherwise use a foreach() loop or the system() function instead. -
For portability, when using features that may not be implemented on every machine, test the construct in an eval to see if it fails. If you know what version or patchlevel a particular feature was implemented, you can test $] ($PERL_VERSION in English) to see if it will be there. The Config module will also let you interrogate values determined by the Configure program when Perl was installed.
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Choose mnemonic identifiers. If you can’t remember what mnemonic means, you’ve got a problem.
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While short identifiers like $gotit are probably ok, use underscores to separate words in longer identifiers. It is generally easier to read $var_names_like_this than $VarNamesLikeThis, especially for non-native speakers of English. It’s also a simple rule that works consistently with VAR_NAMES_LIKE_THIS.
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Package names are sometimes an exception to this rule. Perl informally reserves lowercase module names for "pragma" modules like integer and strict. Other modules should begin with a capital letter and use mixed case, but probably without underscores due to limitations in primitive file systems' representations of module names as files that must fit into a few sparse bytes.
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If you have a really hairy regular expression, use the /x modifier and put in some whitespace to make it look a little less like line noise. Don’t use slash as a delimiter when your regexp has slashes or backslashes.
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Always check the return codes of system calls. Good error messages should go to STDERR, include which program caused the problem, what the failed system call and arguments were, and (VERY IMPORTANT) should contain the standard system error message for what went wrong. Here’s a simple but sufficient example −
opendir(D, $dir) or die "can't opendir $dir: $!";
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Think about reusability. Why waste brainpower on a one-shot when you might want to do something like it again? Consider generalizing your code. Consider writing a module or object class. Consider making your code run cleanly with use strict and use warnings (or -w) in effect. Consider giving away your code. Consider changing your whole world view. Consider… oh, never mind.
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Be consistent.
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Be nice.