<?php

$fname = "textfile.txt";
$data = file_get_contents($fname);          // Load file from disk as string.


if ($_POST['Submit'])                       // Only add the data if Submit is set.
{
    $text = $_POST['update'];
    $text = strip_tags($text);              // Remove any HTML from input.
    $text = str_replace(",", "", $text);    // Remove commas from input.
    $text = explode(" ", $text);            // Split text at every space.

    $to_add = array();                      // List of cleansed words to add to file.

    // Clean the words and check if they're in the file aready.
    foreach ($text as $word)                // Loop through each word...
    {
        $word = trim($word);                // Trim any remaining whitespace (tabs, \r, \n, etc)
        if (empty($word)) { continue; }     // Skip if $word is empty after removing whitespace.

        if (stripos($data, $word) !== FALSE)    // Using stripos, not stristr because we only need to know if it's there.
        {
            echo "'$word' is already in the file.<br />";

        } else {    // Word isn't in the file, add to list of words to write
            $to_add[] = $word;
        }
    }

    // Time to add the words to the file
    $out = fopen($fname, "a");              // Open file for writing *only*, no need for "+"

    foreach ($to_add as $word)
    {
        fwrite($out, $word ."\n");
        echo "Added '$word' to the file.<br />";
    }
    fclose($out);                           // Close the file handle, we're done writing

}

// Regardless of if new data was added, display the file contents in a text box
echo "<textarea>". $data ."</textarea>";

?>