Hi torres09,
please tell me a way so that Working_On.csv should be entered by the user

If what you want is the user responding to "somewhat" like a prompt. The you can do like thus:

use warnings;
use strict;

my $file;

#create an inifite loop
while (1) {

    # ask the user for filename
    print "Enter filename > ";
    chomp( $file = <STDIN> );

    # Exit the loop, if the
    # filename exists and it's a file
    # else redo
    if ( -e $file && -f _ ) {  #Note HERE
        last;
    }
    else { redo }
}

open my $fh, '<', $file or die "can't open file: $!";
...
[download]

Or you check in CPAN for module that does exactly that.
For the file test on the file entered by the user you can check this for more.

Update: Note: If you use Perl 5.9.1 or better, you could actually write: if ( -e -f $file ) { ..