COPY: is a label. It puts a "goto" point before the next statement, so that when you do goto COPY your code will resume at $J=....

If you get rid of the $J=... line, the next line, use File::Copy is actually not a run time statement you can place a label on. It is executed at compile time. Therefore you will get a compilation error. If you move the use File::Copy to the top of the Perl script, it will resolve the compilation error.