MODX snippet to write to a text file.

NotePad.php

<?php
$content = $modx->getOption('content', $scriptProperties, 'eof');
$filename = $modx->getOption('filename', $scriptProperties, 'text.txt');
$filedir = $modx->getOption('filedir', $scriptProperties, 'assets');
$append = $modx->getOption('append', $scriptProperties, false);

$fopen = "w";
if ($append > 0){
$fopen = "a";
};
$fileURL = (string) ($modx->config['base_path']. $filedir .'/'. $filename);

// Let's make sure the file exists and is writable first.
if (is_writable($fileURL)) {
    if (!$handle = fopen($fileURL, $fopen)) {
         echo "Cannot open file ($fileURL)";
         exit;
    }
    // Write $content to our opened file.
    if (fwrite($handle, $content . "\r\n") === FALSE) {
        echo "Cannot write to file ($fileURL)";
        $modx->log(modX::LOG_LEVEL_ERROR,'Cannot write to file '.$fileURL);
        exit;
    }
    // echo "Success, wrote ($content) to file ($fileURL)";
    fclose($handle);
} else {
    $modx->log(modX::LOG_LEVEL_ERROR,'The file '. $fileURL . ' is not writable');
}

return true;

Example usage.

[[!Notepad? &content=`[[#312.content]]` &filename=`product-feed.xml` &filedir=`XML` &result=`success`]]