By using a hash you can avoid scanning the git file multiple times. For example ;

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

my %git=();
my $git_file = "/tmp/git_sorted.log";
open(GIT,'<',$git_file) or die "Really bad $git_file : $!";
while (<GIT>){
  chomp;
  $git{$_}=1;
}
close GIT;
             
my $yum_file = "/tmp/yum_sorted.log";                     
open(YUM,'<',$yum_file) or die "Really, really bad $yum_file : $!";
while (<YUM>){
  chomp;
  if (exists $git{$_}){
    # exists                    
  } else {
    # new 
    print "$_ package not in $git_file\n"; 
  }
}                        
close YUM;
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poj