String in fopen() path

Before I ask the qestion, I'd like to say that the people on this are the best! Several times, readers here have come to my rescue. Many, many thanks. I need to write data files with filenames ending in '.txt', but making each unique with a random number before the '.txt'. No problem gettting the random number with the rand() function, but $newfile=fopen("/htdocs/orders/$worders, "a+"); doesn't work. $worders is a random number with '.txt' appended, so the above would seem to read: $newfile=fopen("/htdocs/orders/2873790.txt, "a+"); ..but, of course, it doesn't work that way. Could someone suggest how to assign a radnomly generated number as the name of a text file being written to disk? Thanks very much, Don Smith