open my $fh, '<', $filename or die "$filename: $!";
while (<$fh>) {
        if (/pattern/) {
                # do something ...
                print $_;
        }
}
close $fh;

##</code><code>##

use warnings;
use strict;
use DateTime;
use DateTime::Format::Strptime;
use Path::Class qw/dir/;

my $LOGPATH = '.';
my $STARTD = '2017-12-08';
my $NUMDAYS = 3;
my $PATTERN = '1.2.3.4';

my $strp = DateTime::Format::Strptime->new(on_error=>'croak',
        pattern => '%Y-%m-%d', time_zone=>'local');
my $dt = $strp->parse_datetime($STARTD);

my @files;
for (1..$NUMDAYS) {
        my $date = $dt->strftime('%Y-%m-%d');
        push @files, sort grep { $_->basename=~/\.log\z/i }
                dir($LOGPATH,$date)->children;
        $dt->add(days=>1);
}

{ # in a new block for "local"
	local *ARGV; @ARGV = @files;
	while (<>) {
	        chomp;
	        if (/\Q$PATTERN\E/) {
	                print "$ARGV:$.: $_\n";
	        }
	} continue { close ARGV if eof }
}