thank you for your reply. I tried your code and it WORKS! thank you very much and thanks for every one who had replied my questions.

by the way, I would like to do some operation to the file, I tried some code like this:

 print "hello 1\n" if (-r $_);
 my @matching = grep {/$my_pattern/} <$_>;
[download]

I failed with this code. I have to

 open $filehandle,"<", $_" or die .... 
 my @matching = grep {/$my_pattern/} <$_>;
[download]

did I do something wrong? or is there any better way to do grep or similar operateion in the $_? thanks.