First off, your files are backwards, there are spaces in the data segments, and it always makes sense to keep the key as part of the data. That said

use strict; use warnings; 
use Data::Dumper;

my %app_map;

readit (\%app_map,'2.csv','name',qw /name leg_len diet/); 
readit (\%app_map,'1.csv','name',qw /name str_len stance/); 

my @result; 
while ( my ($k, $v) = each %app_map ) {
       if(defined($v->{diet}) && $v->{diet} eq 'herbivore'
           && defined($v->{str_len})
          ){ push @result,$v;} 
    
        }

my @sorted=sort {$a->{str_len} <=> $b->{leg_len}} @result; 
for my $row (@sorted) { 
  print $row->{name}.' '.$row->{leg_len}."\n";
  }
#print Dumper \%app_map;

exit; 

sub readit { 
  my $db=shift; 
  my $fn=shift; 
  my $key=shift; 
  my @vars=@_; 
  open my $fh, '<', $fn or die $!;
  my $header1 = <$fh>;
  my $vn=$#vars; 
  while(my $row = <$fh>){
         chomp $row;
         my $h0={}; 
     my @parts= split /\,/, $row;
         for my $ii (0..$vn){ 
           unless (defined ($parts[$ii])) {$parts[$ii]='';} 
           $parts[$ii]=~s/^\s+//; 
           $parts[$ii]=~s/\s+$//; 
           unless ($parts[$ii] eq '') { $h0->{$vars[$ii]}=$parts[$ii];
+ } 
           } 
         my $keyval=$h0->{$key}; 
         my $h1=$db->{$keyval}; 
         unless ($h1) { $db->{$keyval}=$h0; } 
           else { 
             while ( my ($k, $v) = each %$h0 ) {$h1->{$k}=$v;} 
             } # exists 
         } # row 
  close $fh or die $!;
} # readit
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