A simple approach : 


use strict ;
use warnings ; 

my %initial = () ;
my %seen = () ;  # increment if animal is seen 
my $new_value ; 



# Load initial values
open FILE, '<', 'file1.txt' or die 'Failed to open file1' ; 
while ( my $line = <FILE> ) {     
    my ($animal, $count ) = split " ", $line ;
    $initial{$animal}=$count ;
    }
close FILE ;


# Open file to look for new animals
open UPDATE , '<', 'file2.txt' or die 'Failed to open file2' ; 
while ( my $line = <UPDATE> ) {
    # We assume a special pattern form your example file
    my $animal = $1 if $line =~ m/^(\w+) feed/ ;
    $seen{$animal}++ ;
    }
close UPDATE ;


# Open result file for writing
open FILE, '>','file1.txt' or die 'Failed to open file1 for writing';

foreach ( sort keys %initial) {

#Deal with the three possible case : 
#new animal, previously existing but unseen, or existing and seen

    if ( defined $seen{$_} and not defined $initial{$_} ) { 
    
            $new_value = 1
    
    } elsif (  not defined $seen{$_} and defined $initial{$_} ) { 
    
            $new_value = $initial{$_} 
    
    } else { 
            $new_value = $initial{$_} + 1  
    
    } 
    
    print FILE "$_ $new_value\n" ;
    
    
}

close FILE ;

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In reply to Re: update values in one file from another by secret
in thread update values in one file from another by Anonymous Monk

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