使用正则表达式自定义 realpath()答案

【问题标题】：Custom realpath() using regex使用正则表达式自定义 realpath()
【发布时间】：2021-06-14 11:11:04
【问题描述】：

我想创建我的个人 realpath() 函数，它使用正则表达式并且不希望该文件存在。

到目前为止我做了什么

function my_realpath (string $path): string {
    if ($path[0] != '/') {
        $path = __DIR__.'/../../'.$path;
    }
    
    $path = preg_replace("~/\./~", '', $path);
    $path = preg_replace("~\w+/\.\./~", '', $path); // removes ../ from path

    return $path;
}

什么不正确

问题是如果我有这个字符串：

"folders/folder1/folder5/../../folder2"

它只删除第一次出现的（文件夹 5/../）：

"folders/folder1/../folder2"

问题

如何删除（使用正则表达式）后跟相同数量“../”的所有文件夹？

示例

"folders/folder1/folder5/../../folder2" -> "folders/folder2"

"folders/folder1/../../../folder2" -> "../folder2"

"folders/folder1/folder5/../folder2" -> "folders/folder1/folder2"

我们可以告诉正则表达式：“~(\w+){n}/(../){n}~”，n 是贪婪的，但在两组中都相同？

【问题讨论】：

标签： php regex regex-group realpath

【解决方案1】：

您可以使用基于递归的模式，例如

preg_replace('~(?<=/|^)(?!\.\.(?![^/]))[^/]+/(?R)?\.\.(?:/|$)~', '', $url)

请参阅regex demo。详情：

(?<=/|^) - 紧靠左边，必须有 / 或字符串开头（如果字符串作为单独的字符串提供，则等于更高效的 (?<![^/])）
(?!\.\.(?![^/])) - 紧靠右边，不应有 .. 后跟 / 或字符串结尾
[^/]+ - 除了/ 之外的一个或多个字符
/ - 一个 / 字符
(?R)? - 递归整个模式，可选
\.\.(?:/|$) - .. 后跟 / 字符或字符串结尾。

见PHP demo：

$strings = ["folders/folder1/folder5/../../folder2", "folders/folder1/../../../folder2", "folders/folder1/folder5/../folder2"];
foreach ($strings as $url) {
    echo preg_replace('~(?<=/|^)(?!\.\.(?![^/]))[^/\n]+/(?R)?\.\.(?:/|$)~', '', $url) . PHP_EOL;
}
// => folders/folder2, ../folder2, folders/folder1/folder2

或者，您可以使用

(?<![^/])(?!\.\.(?![^/]))[^/]+/\.\.(?:/|$)

请参阅regex demo。详情：

(?<![^/]) - 紧靠左边，必须有字符串开头或/ char
(?!\.\.(?![^/])) - 紧靠右侧，不应有 .. 后跟 / 或字符串结尾
[^/]+ - 除了/ 之外的一个或多个字符
/\.\. - /.. 子字符串后跟...
(?:/|$) - / 或字符串结尾。

见PHP demo：

$strings = ["folders/folder1/folder5/../../folder2", "folders/folder1/../../../folder2", "folders/folder1/folder5/../folder2"];
foreach ($strings as $url) {
    $count = 0;
    do {
        $url = preg_replace('~(?<![^/])(?!\.\.(?![^/]))[^/]+/\.\.(?:/|$)~', '', $url, -1, $count);
    } while ($count > 0);
    echo "$url" . PHP_EOL;
}

preg_replace('~(?<![^/])(?!\.\.(?![^/]))[^/]+/\.\.(?:/|$)~', '', $url, -1, $count) 中的 $count 参数保存替换的次数，并且替换一直进行到找不到匹配项为止。

输出：

folders/folder2
../folder2
folders/folder1/folder2

【讨论】：

【解决方案2】：

您也可以使用非正则表达式方法：

<?php
    
$strings = ["folders/folder1/folder5/../../folder2", "folders/folder1/../../../folder2", "folders/folder1/folder5/../folder2"];
    
function make_path($string) {
    $parts = explode("/", $string);
    $new_folder = [];
    for ($i=0; $i<count($parts); $i++) {
        if (($parts[$i] == "..") and count($new_folder) >= 1) {
            array_pop($new_folder);
        } else {
            $new_folder[] = $parts[$i];
        }
    }
    return implode("/", $new_folder);
}
    
$new_folders = array_map('make_path', $strings);
print_r($new_folders);
?>

这会产生

Array
(
    [0] => folders/folder2
    [1] => ../folder2
    [2] => folders/folder1/folder2
)

见a demo on ideone.com。

【讨论】：