for (@files) {
    open OLDDATA, "< $_"
        or warn 'File does not open: ', $! and next;
    open NEWDATA, "> $_!"
        or warn 'File not open: ', $! and next;

    while (<OLDDATA>) {
        s/aaaaa/FFFFFFF/gi;
        s/bbbbb/EEEEEEE/gi;
        s/cccccc/GGGGGGG/gi;
        print NEWDATA $_;
    }

    close NEWDATA or warn $! and next;
    close OLDDATA or warn $! and next;
    rename "$_!", $_;
}