Earth	Host1
Jupiter	Host2
Venus	Host3
Mars	Host4

##</code><code>##

use Modern::Perl;
use File::Slurp qw/read_file write_file/;

my $logFile = 'log.txt';
my $oldNewFile = 'oldNewFile.txt';

my $text = read_file $logFile;

for(read_file $oldNewFile){
	my ($old, $new) = split;
	$text =~ s/\b$old\b/$new/g
}

say $text;
#write_file( $logFile, $text );