Firstly, 'cp' takes its arguments on the command line. It does nothing with data sent over STDIN. You probably mean to do something like this:

system("cp", "file1", "file2") and die "...";  # system returns false 
+upon success, not true
[download]

Of course, it's only a few lines to repeat this procedure in Perl if you wanted to avoid the system overhead entirely.

Additionally, this statement is incorrect:

print COPY "file1 file2" || die("Could not print to COPY: $!");
[download]

The || operator binds very tightly here (it has a high precedence), so if we were to use parenthesis just about everywhere we could, it would look a bit like this:

print COPY ("file1 file2" || die("..."));
[download]

When making 'or'-type decisions based upon execution, you want to use a lower-precedence operator like 'or' instead of '||'. Only use || when you want to make a decision based upon values, and want to use $value1 || $value2.