How to access content from multiple files

Is there any way that I can add the content of multiple files then put the combined values into one file?

I am currently trying this:

 $start_tr = include 'include_all_items/item_input_start_tr.php' ;   
 $img_start = include 'include_all_items/item_input_img_start.php' ;
 $img_link = include 'include_all_items/item_input_img_link.php' ;
 $img_end = include 'include_all_items/item_input_img_end.php' ;

 $newcontent = "$start_tr
 $link 
 $img_start 
 $_POST[img_link] 
 $img_end ";

 $content = $newcontent.file_get_contents('../../include/item.computer.php');
 file_put_contents('../../include/item.computer.php', $content);

Answer

include is for code, not for content. In your case you have to use file_get_contents so you can save the returned value. include will not give you that value.

include()

Handling Returns: include returns FALSE on failure and raises a warning. Successful includes, unless overridden by the included file, return 1.

 $start_tr = file_get_contents('include_all_items/item_input_start_tr.php');   
 $img_start = file_get_contents('include_all_items/item_input_img_start.php');
 $img_link = file_get_contents('include_all_items/item_input_img_link.php');
 $img_end = file_get_contents('include_all_items/item_input_img_end.php');

Now you can use your variable like you did.

 $newcontent = "$start_tr
 $link 
 $img_start 
 $_POST[img_link] 
 $img_end ";