<https://larryullman.com/forums/index.php?/topic/29-part-3-physical-products-ch8-creating-a-catalog/#comment-293>
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"Why would you remove that? That's the code that's supposed to work. Do you not understand what I mean by \"print out what values the variables have\"? It's critical, fundamental debugging. As I wrote two posts ago, just print out the values of the variables before that line. To be more explicit, add this code to your script (again, before the aforementioned line): \n \n\n\necho \"&lt;p&gt;Type = $type &lt;br /&gt;\nSP Type = $sp_type &lt;br /&gt;\nSP Cat = $sp_cat &lt;br /&gt;\nCategory = $category &lt;/p&gt;\";\n\n \n  \n  \nThat's all I mean. Just print out the values of the variables so you can see what they are. Don't assign values to the variables and don't remove any code, just print out the values of the variables.  \n  \nSince that conditional is true, it means one of those variables doesn't have a proper value. The goal, then, is to determine which. Once you do that, you can work your way backwards to where the variables are assigned values to see where the problem is. \n"
<https://larryullman.com/forums/index.php?/topic/29-part-3-physical-products-ch8-creating-a-catalog/#comment-308>