#!/usr/bin/perl
use strict;
use warnings;

use IO::All;
use Data::Dumper;

foreach my $file (@ARGV) {
    if ( -e $file ) {  # double check existence
	my @lines = io($file)->chomp->slurp; # Chomp as you slurp
	if (my @matches = grep( /string/, @lines ) ) {
	    print "Found in File: '$file':\n";
	    print Dumper \@matches;
	}
    }
}

__END__

$ perl test.pl a.txt b.txt c.txt
Found in File: 'a.txt':
$VAR1 = [
          'Line two interested, string'
        ];
Found in File: 'b.txt':
$VAR1 = [
          'Line one interested, string',
          'Line two interested, string'
        ];

__DATA__

$ cat a.txt b.txt c.txt
Line one not interested
Line two interested, string
Line one interested, string
Line two interested, string
Line one not interested
Line two not interested
Line three not interested