Question

For example:

open (PS , " tail -n 1 $file | grep win " );

I want to find whether the file handle is empty or not.

Answer 1

You can also use eof to check whether a file handle is exhausted. Here is an illustration based loosely on your code. Also note the use of a lexical file handle with the 3-arg form of open.

use strict;
use warnings;

my ($file_name, $find, $n) = @ARGV;

open my $fh, '-|', "tail -n $n $file_name | grep $find" or die $!;

if (eof $fh){
    print "No lines\n";
}
else {
    print <$fh>;
}