How do you think the problem i asked for you? Actually, i tried the following codes using the file::monitor::delta package, finally, it worked very well!

use File::Monitor;
use File::Copy::Recursive qw(fcopy rcopy dircopy fmove rmove dirmove);

my $monitor = File::Monitor->new();

    # Watch some files
    for my $file (qw( 1.doc 2.xls)) {
        $monitor->watch( $file );
        }

    # First scan just finds out about the monitored files. No changes
    # will be reported.
    #$object->scan;
while (1) {
    $monitor->scan;
       sleep 10;
    # After the first scan we get a list of File::Monitor::Delta objec
+ts
    # that describe any changes
    my @changes = $monitor->scan;
    for my $change (@changes) {
        # Call methods on File::Monitor::Delta to discover what change
+d
        if ($change->is_mtime) {
            my $name     = $change->name;
            my $old_mtime = $change->old_mtime;
            my $new_mtime = $change->new_mtime;
            print "$name changed at $new_mtime\n";
            fcopy ("$name","p:\\phdpaper"); #backup automatically for 
+the file which just has been modified
        }
    }
    
 }
[download]

Thank you for your help!