print "Enter a file to look up for: ";
my $file = <STDIN>;
chomp $file; # Get rid of newline character
exit 0 if ($file eq ""); # If empty string, exit.

use File::Find;

my $dir = # whatever you want the starting directory to be

find(\&do_something_with_file, $dir);

sub do_something_with_file
{
    #.....count number of lines of the file and simply concatenate the lines.

    #.....$numlines[$i++] . each line etc. etc.
}