Best way to automatically remove comments from PHP code

Use php -w <sourcefile> to generate a file stripped of comments and whitespace, and then use a beautifier like PHP_Beautifier to reformat for readability.

$fileStr = file_get_contents('file.php');
foreach (token_get_all($fileStr) as $token ) {
    if ($token[0] != T_COMMENT) {
        continue;
    }
    $fileStr = str_replace($token[1], '', $fileStr);
}

echo $fileStr;

I'd use tokenizer. Here's my solution. It should work on both PHP 4 and 5:

$fileStr = file_get_contents('path/to/file');
$newStr  = '';

$commentTokens = array(T_COMMENT);
    
if (defined('T_DOC_COMMENT')) {
    $commentTokens[] = T_DOC_COMMENT; // PHP 5
}

if (defined('T_ML_COMMENT')) {
    $commentTokens[] = T_ML_COMMENT;  // PHP 4
}

$tokens = token_get_all($fileStr);

foreach ($tokens as $token) {    
    if (is_array($token)) {
        if (in_array($token[0], $commentTokens)) {
            continue;
        }
        
        $token = $token[1];
    }

    $newStr .= $token;
}

echo $newStr;

Here's the function posted above, modified to recursively remove all comments from all PHP files within a directory and all its subdirectories:

function rmcomments($id) {
    if (file_exists($id)) {
        if (is_dir($id)) {
            $handle = opendir($id);
            while($file = readdir($handle)) {
                if (($file != ".") && ($file != "..")) {
                    rmcomments($id . "/" . $file); }}
            closedir($handle); }
        else if ((is_file($id)) && (end(explode('.', $id)) == "php")) {
            if (!is_writable($id)) { chmod($id, 0777); }
            if (is_writable($id)) {
                $fileStr = file_get_contents($id);
                $newStr  = '';
                $commentTokens = array(T_COMMENT);
                if (defined('T_DOC_COMMENT')) { $commentTokens[] = T_DOC_COMMENT; }
                if (defined('T_ML_COMMENT')) { $commentTokens[] = T_ML_COMMENT; }
                $tokens = token_get_all($fileStr);
                foreach ($tokens as $token) {
                    if (is_array($token)) {
                        if (in_array($token[0], $commentTokens)) { continue; }
                        $token = $token[1]; }
                    $newStr .= $token; }
                if (!file_put_contents($id, $newStr)) {
                    $open = fopen($id, "w");
                    fwrite($open, $newStr);
                    fclose($open);
                }
            }
        }
    }
}

rmcomments("path/to/directory");