You could do it somewhat smarter and extract just the numbers:

my @numbers = map /object(\d+)000/, grep -d, readdir(DIR);
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You can even directly pull out the highest number by using max out of List::Util:

use List::Util 'max';
my $highest = max map /object(\d+)000/, grep -d, readdir(DIR);
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And using glob instead of readdir can help you wead out the unwanted files before trying to process them, if there's a lot of other stuff in the directory you may be not interested in:

my $highest = max map /object(\d+)000/, grep -d, glob 'object???000';
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