use strict;
use Tie::File;

my $filename = "some.log";
my @file;

tie @file, 'Tie::File', $filename || die "Unable to open file\n";

my $index = 0;
foreach my $line (@file) {
  if ($line =~ m/xyz/i) {
    my $var1 = $file[$index-4];
    my $var2 = $file[$index+4];
    print "Found values '$var1' and '$var2'\n";
  }
  $index++;
}

untie @file;