php 测试字符串是否为正则表达式
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Test if a string is regex
提问by Hosh Sadiq
Is there a good way of test if a string is a regex or normal string in PHP?
有没有一种很好的方法来测试字符串是 PHP 中的正则表达式还是普通字符串？
Ideally I want to write a function to run a string through, that returns true or false.
理想情况下，我想编写一个函数来运行一个字符串，该函数返回 true 或 false。
I had a look at preg_last_error():
我看了看preg_last_error()：
<?php
preg_match('/[a-z]/', 'test');
var_dump(preg_last_error());
preg_match('invalid regex', 'test');
var_dump(preg_last_error());
?>
Where obviously first one is not an error, and second one is. But preg_last_error()returns int 0both times.
显然第一个不是错误，第二个是。但是两次都preg_last_error()返回int 0。
Any ideas?
有任何想法吗？
采纳答案by ThiefMaster
The only easy way to test if a regex is valid in PHP is to use it and check if a warning is thrown.
测试正则表达式在 PHP 中是否有效的唯一简单方法是使用它并检查是否抛出警告。
ini_set('track_errors', 'on');
$php_errormsg = '';
@preg_match('/[blah/', '');
if($php_errormsg) echo 'regex is invalid';
However, using arbitrary user input as a regex is a bad idea. There were security holes (buffer overflow => remote code execution) in the PCRE engine before and it might be possible to create specially crafted long regexes which require lots of cpu/memory to compile/execute.
然而，使用任意用户输入作为正则表达式是一个坏主意。之前在 PCRE 引擎中存在安全漏洞（缓冲区溢出 => 远程代码执行），可能会创建特制的长正则表达式，需要大量 CPU/内存来编译/执行。
回答by Niet the Dark Absol
The simplest way to test if a string is a regex is:
测试字符串是否为正则表达式的最简单方法是：
if( preg_match("/^\/.+\/[a-z]*$/i",$regex))
This will tell you if a string has a good chance of being intended to be as a regex. However there are many string that would pass that check but fail being a regex. Unescaped slashes in the middle, unknown modifiers at the end, mismatched parentheses etc. could all cause problems.
这将告诉您字符串是否很有可能用作正则表达式。但是，有许多字符串可以通过该检查但不能成为正则表达式。中间未转义的斜杠、末尾的未知修饰符、不匹配的括号等都可能导致问题。
The reason preg_last_errorreturned 0 is because the "invalid regex" is not:
preg_last_error返回 0的原因是因为“无效的正则表达式”不是：
- PREG_INTERNAL_ERROR (an internal error)
- PREG_BACKTRACK_LIMIT_ERROR (excessively forcing backtracking)
- PREG_RECURSION_LIMIT_ERROR (excessively recursing)
- PREG_BAD_UTF8_ERROR (badly formatted UTF-8)
- PREG_BAD_UTF8_OFFSET_ERROR (offset to the middle of a UTF-8 character)
- PREG_INTERNAL_ERROR（内部错误）
- PREG_BACKTRACK_LIMIT_ERROR（过度强制回溯）
- PREG_RECURSION_LIMIT_ERROR（过度递归）
- PREG_BAD_UTF8_ERROR（UTF-8 格式错误）
- PREG_BAD_UTF8_OFFSET_ERROR（偏移到 UTF-8 字符的中间）
回答by ya_dimon
Here is a good answer how to:
这是一个很好的答案如何：
https://stackoverflow.com/a/12941133/2519073
https://stackoverflow.com/a/12941133/2519073
if(@preg_match($yourPattern, null) === false){
//pattern is broken
}else{
//pattern is real
}
回答by Ben
Why not just use...another regex? Three lines, no @kludges or anything:
为什么不使用...另一个正则表达式？三行，没有@杂乱无章或任何东西：
// Test this string
$str = "/^[A-Za-z ]+$/";
// Compare it to a regex pattern that simulates any regex
$regex = "/^\/[\s\S]+\/$/";
// Will it blend?
echo (preg_match($regex, $str) ? "TRUE" : "FALSE");
Or, in function form, even more pretty:
或者，在函数形式中，甚至更漂亮：
public static function isRegex($str0) {
$regex = "/^\/[\s\S]+\/$/";
return preg_match($regex, $str0);
}
This doesn't test validity; but it looks like the question is Is there a good way of test if a string is a regex or normal string in PHP?and it does do that.
这不会测试有效性；但看起来问题是Is there a good way of test if a string is a regex or normal string in PHP?，它确实做到了。
