PHP教程：高效从URL路径中提取倒数第二个片段

<?php
$url_string = "https://localhost/categories/post_12345678/a25d48aff";
$parsed_url = parse_url($url_string);

// 检查是否成功解析且包含路径
$path = $parsed_url['path'] ?? ''; // 结果可能是 /categories/post_12345678/a25d48aff

echo "原始路径: " . $path . "\n";
?>

<?php
// 承接上一步的 $path
$cleaned_path = trim($path, '/'); // 结果是 categories/post_12345678/a25d48aff

echo "清理后的路径: " . $cleaned_path . "\n";
?>

<?php
// 承接上一步的 $cleaned_path
$path_segments = explode("/", $cleaned_path);
/*
对于 "categories/post_12345678/a25d48aff"，结果类似:
Array
(
    [0] => categories
    [1] => post_12345678
    [2] => a25d48aff
)
*/
echo "路径片段数组: \n";
print_r($path_segments);
?>

<?php
// 承接上一步的 $path_segments
$reversed_segments = array_reverse($path_segments);
/*
对于上述示例，反转后的数组类似:
Array
(
    [0] => a25d48aff
    [1] => post_12345678
    [2] => categories
)
*/
$second_to_last_segment = $reversed_segments[1]; // 结果是 post_12345678

echo "倒数第二个片段: " . $second_to_last_segment . "\n";
?>

<?php
/**
 * 从URL路径中提取倒数第二个片段
 *
 * @param string $url_string 待处理的URL字符串
 * @return string|null 如果成功提取则返回片段，否则返回null
 */
function getSecondToLastUrlSegment(string $url_string): ?string
{
    $parsed_url = parse_url($url_string);

    // 检查URL是否有效且包含路径
    if (!isset($parsed_url['path'])) {
        return null;
    }

    $path = trim($parsed_url['path'], '/');

    // 如果路径为空或只有根目录，则无有效片段
    if (empty($path)) {
        return null;
    }

    $path_segments = explode("/", $path);

    // 检查是否有足够的片段来获取倒数第二个
    // 至少需要两个片段才能有倒数第二个（例如 "segment1/segment2"）
    if (count($path_segments) < 2) {
        return null;
    }

    // 反转数组并获取索引为1的元素（原倒数第二个）
    return array_reverse($path_segments)[1];
}

// 示例用法
$url1 = "https://localhost/categories/post_12345678/a25d48aff";
$segment1 = getSecondToLastUrlSegment($url1);
echo "URL: " . $url1 . "\n";
echo "提取的片段: " . ($segment1 ?? "未找到") . "\n\n"; // 输出: post_12345678

$url2 = "https://example.com/item/123";
$segment2 = getSecondToLastUrlSegment($url2);
echo "URL: " . $url2 . "\n";
echo "提取的片段: " . ($segment2 ?? "未找到") . "\n\n"; // 输出: 123

$url3 = "https://example.com/onlyone"; // 只有一个片段
$segment3 = getSecondToLastUrlSegment($url3);
echo "URL: " . $url3 . "\n";
echo "提取的片段: " . ($segment3 ?? "未找到") . "\n\n"; // 输出: 未找到

$url4 = "https://example.com/"; // 无有效片段
$segment4 = getSecondToLastUrlSegment($url4);
echo "URL: " . $url4 . "\n";
echo "提取的片段: " . ($segment4 ?? "未找到") . "\n\n"; // 输出: 未找到

$url5 = "invalid-url"; // 无效URL
$segment5 = getSecondToLastUrlSegment($url5);
echo "URL: " . $url5 . "\n";
echo "提取的片段: " . ($segment5 ?? "未找到") . "\n\n"; // 输出: 未找到
?>