根据复选框值向文件添加字段

I am doing a PHP assignment where I am getting input that uses some checkboxes and stores the information in a file.

Let's say I have a checkbox

 Active: <input type="checkbox" name="preference" value="Pepperoni" checked="checked>

When I say something like:

$Preference1 = $_POST['preference'];

What is stored in $Preference1? Does it store information that tells whether the box was checked or not, or does it contain "Pepperoni"? Is there a way to check to see if a box is checked? Like,

Pesudocode

if Preference1 is checked
   add Pepperoni to the file;

if Preference2 is checked
   add Sausage to the file;

I did work with radio buttons but those are a bit different since only one of those can be checked at a time, but for checkboxes, multiples boxes and be selected. Is there a way to see if a button is checked and if so, how would I do that? Thanks.

UPDATE After doing some digging around I found a post that did something like this:

$('#isAgeSelected').attr('checked')

But that is using jQuery. Would something like the .attr work in PHP? Could I say something like

if($_POST['preference'].attr("checked"))
   //do whatever

Does this work in PHP?

In this case you can try with store values into an single array. So you can track with multiple value that has been checked.

<?php
if(isset($_POST['submit']) &&  $_POST['submit']== 'submit'){
    if(isset($_POST['preference']) && count($_POST['preference']>0)){
        echo"<pre>";print_r($_POST['preference']);
    } else {
        echo "Empty";
    }

}

?>
<form name='myForm' method='post'>
<input type="checkbox" name="preference[]" value="Pepperoni" >
<input type="checkbox" name="preference[]" value="Pepperoni1" >
<input type="checkbox" name="preference[]" value="Pepperoni2">
<input type='submit' name='submit' value='submit'>
</form>

Check this link. Something like:

if (isset($_POST['preference'])) {

    // Checkbox is selected
} else {

   // Alternate code
}

$Preference1 = $_POST['preference'] = "Pepperoni" //value from < input > tag

To check if box is checked, you have to check if $_POST['preference'] is set and is not NULL.

if (isset($_POST['preference'])) {
    echo "Checkbox is selected";
}