#!/usr/bin/perl
use strict;
use warnings;
use Tie::File;
use File::Find;

my @directories_to_search = ("/some/dir_name");
find(\&wanted, @directories_to_search);

sub wanted {
	if (-f) {
		tie my @array, 'Tie::File', $_ or die $!;
		s/\$Log/\$History/gi for @array;
	}
}