我的意思(H,M,美元$ S)日期= $ = ~ M { ^([0 - 9]{ 2 }):([0 - 9]{ 2 }):([0 - 9]{ 2 })}在perl

I am new to perl. Can anyone explain the meaning of the following line of code:

我是perl新手。谁能解释下面一行代码的含义:

my ($H,$M,$S) = $date =~ m{^([0-9]{2}):([0-9]{2}):([0-9]{2})}

I assume that after the execution of this line $H, $M and $S will have the values extracted from $date. Can anyone explain to get a better understanding?

我假设在执行这一行$H之后，$M和$S将提取$date中的值。谁能解释一下以便更好地理解?

3 个解决方案

#1

It tries to match the contents of the $date variable, with a regex:

它试图匹配$date变量的内容，并使用regex:

^([0-9]{2}):([0-9]{2}):([0-9]{2})

The regex basically means: from the start of the string, there should be two digits and colons repeated three times. Each of these three two digit numbers are enclosed in a group.

regex的基本意思是:从字符串开始，应该有两个数字和冒号重复三次。这三个两位数中的每一个都包含在一个组中。

Finally, the matches of the three groups are assigned to local variables $H, $M and $S.

最后，将这三组的匹配分配给本地变量$H、$M和$S。

For example if

$date = "10:37:21 2016.01.02";

then

然后

$H = "10";
$M = "37";
$S = "21";

#2

Can anyone explain to get a better understanding?

谁能解释一下以便更好地理解?

You need to start to be aware of two things:

你需要开始意识到两件事:

list context

上下文列表
scalar context

标量上下文

The match operator, m//, will provide different results depending on what's on the left hand side of your = sign. Check this out:

匹配操作符m// /将根据=符号的左边提供不同的结果。看看这个:

use strict;
use warnings; 
use 5.020;

my $result =  "abc" =~ m/a(.)(.)/;
say $result;   #=> 1

my @results = "abc" =~ m/a(.)(.)/;
for my $result (@results) {
    say $result;
};

--output:--
b
c

A $variable can only store one thing, so when there is a $variable on the left hand side of the = sign, the $variable looks over to the match operator, m//, on the right hand side of the = sign and calls out, "Hey, I can only store one thing over here, just give me one thing, please!" The match operator responds by returning 1, for true, if there was a match; or 0, for false, if there wasn't a match.

美元变量只能存储一件事,所以,当有一个美元变量放在等号的左边,$变量看起来匹配算子,m / / =右边的标志和电话,“嘿,我只能存储一件事,给我一件事,请!”匹配操作符的响应是返回1，如果存在匹配，则为true;如果没有匹配，则为0。

On the other hand, when an @variable is on the left hand side of the = sign, the array looks over to the m// operator and calls out, "Hey, I can store a bunch of things over here, so give me a bunch of stuff, please!" The match operator responds by returning what matched the capture groups in the regex if there was a match; if there wasn't a match, the match operator returns ().

另一方面，当@变量在=符号的左边时，数组会向m//运算符查找，并调用:“嘿，我可以在这里存储很多东西，所以请给我一堆东西!”匹配操作符通过返回匹配regex中的捕获组的内容作为响应;如果没有匹配，匹配操作符返回()。

In the first case, the $variable is said to provide scalar context for the match operator. In the second case, the @variable is said to provide list context for the match operator. Don't let those terms scare you. You know what they mean now.

在第一种情况下，$变量被称为为match操作符提供标量上下文。在第二种情况下，@variable被称为为match操作符提供列表上下文。不要让这些术语吓到你。你知道他们现在的意思。

Next, when you write this:

接下来，当你写下这些:

my ($H,$M,$S) =

You are creating several variables on the left hand side of the = sign. In unison, they call out to the match operator on the other side of the = sign, "Hey, there are many of us over here, give us the bunch of stuff, please! That particular my syntax provides a list context for the match operator which is on the right hand side of the = sign:

您正在=符号的左边创建几个变量。他们异口同声地对=号另一边的报务员喊道:“嘿，这儿有很多人，请把这些东西给我们!”这个特殊的my语法为match操作符提供了一个列表上下文，它位于=号的右边:

my ($group1, $group2) = "abc" =~ m/a(.)(.)/;
say $group1;  #=> b
say $group2;  #=> c

Note that if the delimiters you use for the match operator are m/.../, then you don't have to write the leading m, so typically you will see the example above written as:

注意，如果您用于匹配操作符的分隔符是m/…/，这样你就不用写前导m了，所以通常你会看到上面的例子是这样写的:

my ($group1, $group2) = "abc" =~ /a(.)(.)/;

When you use braces like you did: m{...}{...}, then you have to write the leading m.

当你使用像你这样的牙套时:……}，然后写出前导m。

#3

You can use a simpler regex, which is easier to understand, to do what you want:

你可以使用更简单的正则表达式，更容易理解，做你想做的:

 \d{2}  #\d means a digit, {2} means twice,
        #so this matches two consecutive digits

Here's how you can use that regex:

以下是如何使用regex:

#Just blindly use all three of these in every program:
use strict;
use warnings; 
use 5.020;    

my $date = "10:37:21 2016.01.02";

my ($H,$M,$S) = $date =~ /\d{2}/g;  #g => global, Find all matches in the string

say $H;  #say() is the same as print() with a newline at the end
say $M;
say $S;

--output:--
10
37
21

The regex starts at the beginning of the string and looks for two consecutive digits and finds 10, so that is a match; then the regex jumps over the : and finds 37, so that is a match; then the regex jumps over the : and finds 21, so that is a match; etc., etc.

regex从字符串的开始处开始，查找两个连续的数字，然后找到10，所以这是一个匹配;然后regex跳过:并找到37，因此这是一个匹配;然后regex跳过:并找到21，因此这是一个匹配;等等,等等。

When you assign all the matches to three variables, the first three matches are assigned to the three variables, and the rest of the matches are discarded.

当您将所有匹配分配给三个变量时，前三个匹配被分配给这三个变量，其余的匹配被丢弃。

#1