排骨澄清 [英] Clarification on chomp
问题描述
我现在正在放假，决定花时间学习Perl.我正在使用Beginning Perl( http://www.perl.org/books/beginning- perl/)，我将在第三章结尾处完成练习.
I'm on break from classes right now and decided to spend my time learning Perl. I'm working with Beginning Perl (http://www.perl.org/books/beginning-perl/) and I'm finishing up the exercises at the end of chapter three.
其中一项练习要求我将您的重要电话号码存储在哈希中.编写一个程序，以该人的姓名查找号码."
One of the exercises asked that I "Store your important phone numbers in a hash. Write a program to look up numbers by the person's name."
无论如何，我想出了这个:
Anyway, I had come up with this:
#!/usr/bin/perl
use warnings;
use strict;
my %name_number=
(
Me => "XXX XXX XXXX",
Home => "YYY YYY YYYY",
Emergency => "ZZZ ZZZ ZZZZ",
Lookup => "411"
);
print "Enter the name of who you want to call (Me, Home, Emergency, Lookup)", "\n";
my $input = <STDIN>;
print "$input can be reached at $name_number{$input}\n";
那是行不通的.我不断收到此错误消息:
And it just wouldn't work. I kept getting this error message:
在连接(.)或hello.plx中的字符串中使用未初始化的值 第17行，第1行
Use of uninitialized value in concatenation (.) or string at hello.plx line 17, line 1
我尝试了一些更多的代码，但是每个解决方案"看起来都比之前的解决方案"复杂.最后，我决定检查答案.
I tried playing around with the code some more but each "solution" looked more complex than the "solution" that came before it. Finally, I decided to check the answers.
我的代码和答案之间的唯一区别是在<STDIN>;之后出现了chomp ($input);.
The only difference between my code and the answer was the presence of chomp ($input); after <STDIN>;.
现在，作者在先前的示例中使用了chomp，但是他并没有真正涵盖chomp的工作.因此，我在www.perlmeme.org上找到了这个答案:
Now, the author has used chomp in previous example but he didn't really cover what chomp was doing. So, I found this answer on www.perlmeme.org:
chomp()函数将(通常)从中删除任何换行符 字符串的结尾.我们通常说的原因是它实际上 删除与当前$/值匹配的任何字符(输入 记录分隔符)，$/默认为换行符.
The
chomp()function will remove (usually) any newline character from the end of a string. The reason we say usually is that it actually removes any character that matches the current value of$/(the input record separator), and$/defaults to a newline..
无论如何，我的问题是:
Anyway, my questions are:
-
正在删除哪些换行符? Perl是否会自动将
"\n"附加到<STDIN>的输入中?我只是有点不清楚，因为当我读到它实际上删除了与$/的当前值匹配的任何字符"时，我不禁想到我不记得在代码中的任何地方放置$/了" ."
What newlines are getting removed? Does Perl automatically append a
"\n"to the input from<STDIN>? I'm just a little unclear because when I read "it actually removes any character that matches the current value of$/", I can't help but think "I don't remember putting a$/anywhere in my code."
我想尽快制定最佳实践-是始终在<STDIN>之后始终包含chomp还是在不必要的情况下?
I'd like to develop best practices as soon as possible - is it best to always include chomp after <STDIN> or are there scenarios where it's unnecessary?
推荐答案
<STDIN>读取到输入字符串的末尾，如果按回车键，则包含换行符.您可能会这样做.
<STDIN> reads to the end of the input string, which contains a newline if you press return to enter it, which you probably do.
chomp删除字符串末尾的换行符. $/是您可能不必担心的变量(如您所见，默认为换行符).它只是告诉perl输入记录分隔符"是什么，我假设这意味着它定义了<FILEHANDLE>读取的距离.您现在几乎可以忘记它，这似乎是一个高级话题.只是假装chomp排在结尾的换行符即可.老实说，我以前从未听说过$/.
chomp removes the newline at the end of a string. $/ is a variable (as you found, defaulting to newline) that you probably don't have to worry about; it just tells perl what the 'input record separator' is, which I'm assuming means it defines how far <FILEHANDLE> reads. You can pretty much forget about it for now, it seems like an advanced topic. Just pretend chomp chomps off a trailing newline. Honestly, I've never even heard of $/ before.
对于您的其他问题，通常不选变量，以后再根据需要添加换行符通常是更清洁的方法，因为您并不总是知道变量是否具有换行符.通过总是剔除变量，您总是会得到相同的行为.在某些情况下，它是不必要的，但是如果您不确定chomp它不会对您造成伤害.
As for your other question, it is generally cleaner to always chomp variables and add newlines as needed later, because you don't always know if a variable has a newline or not; by always chomping variables you always get the same behavior. There are scenarios where it is unnecessary, but if you're not sure it can't hurt to chomp it.
希望这会有所帮助！
这篇关于排骨澄清的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
