从PHP表单提交选中的选项

I'm trying to figure out how to send checked options from a series of checkboxes to a text file that keeps track of what has been selected. The most I have right now is this.

<html>
<?php
//Get contents from zmzonSongs.txt file, put into array.
$songList = explode("
", file_get_contents('zmzonSongs.txt'));

print "Welcome to Zmzon.  Select songs below to add to your library.";
//Print contents as checklist.
foreach($songList as $songs){
    echo "<br/><input type='checkbox' name='songList[]' value='$songs' />"$songs<br>";
}

?>

</html>

I need to send the values of everything that has been checked to a file like myLibrary.txt after the user hits a submit button, but every time I try adding a submit button using the echo command, my entire page stops working and comes up blank. I'm completely lost.

You have an extra quote:

echo "<br/><input type='checkbox' name='songList[]' value='$songs' />"$songs<br>";

should be

echo "<br/><input type='checkbox' name='songList[]' value='$songs' />$songs<br>";

or

echo "<br/><input type='checkbox' name='songList[]' value='$songs' />".$songs."<br>";

Your checkboxes and submit button should be inside a form and your submit-button is HTML, not PHP.

<?php 
    /* Lets set the destination to the same file as the form. (see form action)
     * That means, if someone has submitted the form, there will be data inside 
     * $_POST right now! 
     */
    // var_dump( $_POST );  <-- Can be used to quickly peek inside $_POST

    if ( !empty( $_POST ) )  // Check if there is any data
    {
       save_data_to_file( $_POST ); // pseudo-code (should be replaced by you) 
       echo "success!";  // A success message perhaps?
       exit();  // Stop here to not display the form below.
    }

    // If we come this far, it means the form has not been submitted. 
    // So lets display the form!

    // You can have this line first in the file, or later, 
    // as long as you do this before you try to use it in your checkboxes.
    $songList = explode("
", file_get_contents('zmzonSongs.txt'));
?>

<h1>Welcome to Zmzon.  Select songs below to add to your library</h1>
<form action="thisfile.php" method="POST"> 
    <?php 
        // See, you can jump between PHP and HTML whenever you want.
        foreach($songList as $songs){ 
            echo "<input type='checkbox' ... ><br>";
        }
    ?>
    <input type="submit">
</form>

You can send the data to another page or the same page, decided by "action". The data will be inside a variable $_POST or $_GET (depending on what sending method you choose.)

An easy way to look at those global variables is to use var_dump(). For example:

<pre>
<?php var_dump($_POST); ?>

updated again

<html>
<form method='post'>
<?php
//Get contents from zmzonSongs.txt file, put into array.
if (!isset ($_POST['songList']))
{
   $songList = explode("
", file_get_contents('zmzonSongs.txt'));
  print "Welcome to Zmzon.  Select songs below to add to your library.";
  //Print contents as checklist.
  foreach($songList as $songs){
      echo "<br/><input type='checkbox' name='songList[]' value='$songs' />"$songs<br>";
    }
}
else
{
 $songlist = $_POST['songList']; // which is array
// next you write code to update in text file.

}

?>
<input type="Submit" value="Submit">

</form>
</html>