php preg_match 中的符号是什么意思？
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What do the symbols mean in preg_match?
提问by marciokoko
I have this expression in a code snippet i borrowed offline. It forces the new users to have a password that not only requires upper+lower+numbers but they must be in that order! If i enter lower+upper+numbers, it fails!
我在离线借用的代码片段中有这个表达式。它强制新用户拥有一个密码，不仅需要大号+小号+数字，而且必须按该顺序！如果我输入较低+较高+数字，则失败！
if (preg_match("/^.*(?=.{4,})(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z]).*$/", $pw_clean, $matches)) {
Ive searched online but can't find a resource that tells me what some characters mean. I can see that the pattern is preg_match("/some expression/",yourstring,your match).
我在网上搜索过，但找不到可以告诉我某些字符含义的资源。我可以看到模式是 preg_match("/some expression/",yourstring,your match)。
What do these mean:
这些是什么意思：
1. ^ - ???
2. .* - ???
3. (?=.{4,}) - requires 4 characters minimum
4. (?.*[0-9]) - requires it to have numbers
5. (?=.*[a-z])- requires it to have lowercase
6. (?=.*[A-Z])- requires it to have uppercase
7. .*$ - ???
回答by ccondrup
Here are the direct answers. I kept them short because they won't make sense without an understanding of regex. That understanding is best gained at regular-expressions.info. I advise you to also try out the regex helper toolslisted there, they allow you to experiment - see live capturing/matching as you edit the pattern, very helpful.
以下是直接答案。我让它们简短，因为如果不了解正则表达式，它们就没有意义。这种理解最好在regular-expressions.info 上获得。我建议您也尝试一下那里列出的正则表达式助手工具，它们允许您进行实验 - 在您编辑模式时查看实时捕获/匹配，非常有帮助。
1: The caret ^is an anchor, it means "the start of the haystack/string/line".
1：插入符号^是一个锚点，意思是“大海捞针/字符串/行的开始”。
- If a caret is the first symbol inside a character class
[], it has a different meaning: It negates the class. (So in[^ab]the caret makes that class match anything which is notab)
- 如果插入符号是字符类中的第一个符号
[]，则它具有不同的含义：它否定类。（所以在[^ab]插入符号中使该类匹配任何不是ab 的东西）
2: The dot .and the asterisk *serve two separate purposes:
2：点.和星号*有两个不同的目的：
- The dot matches any single character except newline
\n. - The asterisk says "allow zero or many of the preceeding type".
- 点匹配除换行符之外的任何单个字符
\n。 - 星号表示“允许零个或多个前面的类型”。
When these two are combined as .*it basically reads "zero or more of anything until a newline or another rule comes into effect".
当这两个组合在一起时，.*它基本上读作“零个或多个任何内容，直到换行符或其他规则生效”。
7: The dollar $is also an anchor like the caret, with the opposite function: "the end of the haystack".
7：美元$也是像脱字符号一样的锚，功能相反：“大海捞针”。
Edit:
编辑：
Simple parentheses ( )around something makes it a group. Here you have (?=)which is an assertion, specifically a positive look ahead assertion. All it does is check whether what's inside actually exists forward from the current cursor position in the haystack. Still with me?
Example:foo(?=bar)matches fooonly if followed by bar. baris never matched, only foois returned.
( )一些东西周围的简单括号使它成为一个组。这里你有(?=)which 是一个断言，特别是一个积极的前瞻断言。它所做的只是检查从 haystack 中当前光标位置向前的内容是否确实存在。还在我这儿？
例如：foo(?=bar)匹配foo仅当随后bar。bar永远不会匹配，只会foo返回。
With this in mind, let's dissect your regex:
考虑到这一点，让我们剖析您的正则表达式：
/^.*(?=.{4,})(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z]).*$/
Reads as:
^.* From Start, capture 0-many of any character
(?=.{4,}) if there are at least 4 of anything following this
(?=.*[0-9]) if there is: 0-many of any, ending with an integer following
(?=.*[a-z]) if there is: 0-many of any, ending with a lowercase letter following
(?=.*[A-Z]) if there is: 0-many of any, ending with an uppercase letter following
.*$ 0-many of anything preceding the End
You say the order of password characters matter - it doesn't in my tests. See test script below. Hope this cleared up a thing or two. If you are looking for another regex which is a bit more forgiving, see regex password validation
您说密码字符的顺序很重要 - 在我的测试中并不重要。请参阅下面的测试脚本。希望这能澄清一两件事。如果您正在寻找另一个更宽容的正则表达式，请参阅正则表达式密码验证
<pre>
<?php
// Only the last 3 fail, as they should. You claim the first does not work?
$subjects = array("aaB1", "Baa1", "1Baa", "1aaB", "aa1B", "aa11", "aaBB", "aB1");
foreach($subjects as $s)
{
$res = preg_match("/^.*(?=.{4,})(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z]).*$/", $s, $matches);
echo "result: ";
print_r($res);
echo "<br>";
print_r($matches);
echo "<hr>";
}
Excellent online tool for checking and testing Regular Expressions: https://regex101.com/
用于检查和测试正则表达式的优秀在线工具：https: //regex101.com/
回答by futureelite7
If you don't know this site, you should go there immediately.
如果你不知道这个网站，你应该马上去那里。
This is like the bible of regular expressions.
这就像正则表达式的圣经。
回答by Kathir
To use regular expressions first you need to learn the syntax. This syntax consists in a series of letters, numbers, dots, hyphens and special signs, which we can group together using different parentheses.
要首先使用正则表达式，您需要学习语法。这种语法由一系列字母、数字、点、连字符和特殊符号组成，我们可以使用不同的括号将它们组合在一起。
Look at this link Getting Started with PHP Regular Expressions. An easy way to learn regular expressions.
查看此链接PHP 正则表达式入门。学习正则表达式的简单方法。
