foreach(@files) {
   system("c:\\midicsv\\midicsv.exe", "c:\\midicsv\\newmidi\\$_", "c:\\midicsv\\newcsv\\$_")
}

##</code><code>##

my $file = "C:\\temp\\somefile.csv";
my $midfile = $file; # copy it
$midfile =~ s/\.csv$/.mid/i;