my $time_ = localtime;
my $date = ParseDate($time_);
$date =~ s/://g;
my $unix_date = UnixDate($date, @d_format);
$unix_date =~ s/ //g;
$ash_{date} = $unix_date;
$ash_{temp} = gct();
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What does @d_format contain?   Why put the spaces in the format string and then just remove then?   You should probably use POSIX::strftime, for example:

use POSIX 'strftime';
$ash_{date} = strftime $d_format[0], localtime;
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my %cash = build_comp_hash();
push @aoh, { %cash };
graphable_arrays();
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Why are you copying the hash twice?   Just copy it once:

push @aoh, { build_comp_hash() };
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@xdata = ();
@ydata = ();
my($i, $datum);
for $i (0 .. $#aoh){
  for $datum (keys %{ $aoh[$i] }){
    if($datum =~ m/date/){   
     push @xdata, $aoh[$i]{$datum};
    }
    elsif($datum =~ m/temp/){
     push @ydata, $aoh[$i]{$datum};
    }
    else{}
   }
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It looks like your keys exactly match 'date' and 'temp' so there is no need to iterate through all the keys to find them:

@xdata = ();
@ydata = ();

for my $hash ( @aoh ) {
    push @xdata, $hash->{ date };
    push @ydata, $hash->{ temp };
    }
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