Script that helps to detect broken links in md files (specifically - laravel/docs)

check-anchors.php

<?php

/**
 * Parses *.md files in the current directory for broken links.
 * - [Link](#broken-anchor) without <a name="broken-anchor"></a> within the same file
 * - [Link](another-file#broken-anchor) without <a name="broken-anchor"></a> in the another-file.md
 */

$ok = $fail = 0;

foreach (glob('*.md') as $file) {
    if ($brokenLinks = findBrokenLinks($file)) {
        printError($file, $brokenLinks);
        $fail++;
    } else {
        printOk($file, $brokenLinks);
        $ok++;
    }
}

print PHP_EOL . "OK: {$ok}. FAIL: {$fail}.";

function findBrokenLinks($file)
{
    $contents = file_get_contents($file);

    // Find all the links
    preg_match_all('/\[[^]]+\]\(([-a-z0-9#]+)\)/', $contents, $links);

    // Exclude external links
    $links = array_filter($links[1], function ($link) {
        return 'http' !== substr($link, 0, 4) && 'ftp' !== substr($link, 0, 3);
    });

    // Filter broken links
    return array_filter($links, function ($link) use ($contents) {
        if ('#' !== substr($link, 0, 1)) {
            [$file, $link] = parseFileData($link);

            // if the link was [Link](another-file) without an achor then just check file existance
            if (is_null($link)) {
                return !file_exists($file);
            }

            $contents = file_get_contents($file);
        } else {
            $link = substr($link, 1);
        }

        return false === strpos($contents, "<a name=\"{$link}\"></a>");
    });
}

function parseFileData($link)
{
    $linkData = explode('#', $link);

    $link = $linkData[1] ?? null;
    $file = "{$linkData[0]}.md";

    return [
        file_exists($file) ? file_get_contents($file) : null,
        $linkData[1] ?? null
    ];
}

function printOk($file, $links)
{
    printInfo($file, $links, "OK", "\033[32m");
}

function printError($file, $links)
{
    printInfo($file, $links, "FAIL", "\033[31m");
}

function printInfo($file, $links, $caption = "INFO", $color = "\033[0m")
{
    $default = "\033[0m";

    print "[{$color}{$caption}{$default}] {$file}" . PHP_EOL;
    foreach ($links as $link) {
        print " - {$link}" . PHP_EOL;
    }
}