put file [name+dir]  in php variable when upload button clicked

i have some problem with sending ajax in my wordpress and i have to modify the plugin code manually  like $pathinfo[dirname] or $file[name] and like these and put them into a SESSION and echo it in another page but it didn't work !some thimes SESSION was set and some other neither!can you help me where should write what php code to pull out the filename or full address!