There's no compilation going on here. It's reading files and writing them, without any consideration about whether it's PHP or delimiter-separated variables.
Because there's no consideration for what syntax there might be in the files, there's no guarantee that the resulting file will be syntactically valid. If you execute that there's likely to be problems.
You'll also get problems if you try to read the files from a URL instead of a filename, because then if you're lucky you'll get the results of executing the file, not the file itself.