#!/usr/bin/perl
use strict;
use IO::All;
use warnings;
use Data::Dumper;
use File::Find::Rule;

my @LogDirs = ('/home/user/PerlMonks/',
	       '/tmp/Monks'); # add more here

my $level = shift // 3; # level to dig into
my @files = File::Find::Rule->file()
    ->name( '*.txt', '*.log' ) #can insert regex too
    ->maxdepth($level)
    ->in(@LogDirs);

my %hash;
foreach my $file (@files) {
    my @lines = io($file)->chomp->slurp;
    my $matches = grep {/Start/ or /middle/ or /end/} @lines;
    $hash{$file} = $matches;
}

print Dumper \%hash;

__END__

$ perl test.pl
$VAR1 = {
          '/home/user/PerlMonks/Foo/Bar/monks.log' => 1,
          '/home/user/PerlMonks/sample.txt' => 1,
          '/tmp/Monks/SampleDir/monks.log' => 2
        };

##</code><code>##

$ cat /tmp/Monks/SampleDir/monks.log 
Start line key line.
Ignore this line.
Another line key end.

$ cat /home/user/PerlMonks/Foo/Bar/monks.log
This is line 1.
This key line end.

$ cat /home/user/PerlMonks/sample.txt
This is another key line middle point.
I do not care about this.