There's no need to use no warnings 'uninitialized';---just initialize the array. Remember, too, that the 1st arg to each must be a hash.

I tried your script in a slightly different way. I used a hash because I wanted to keep each.

#!/usr/perl/bin/perl

use Modern::Perl;

$|=1;

my($data) = '/root/Desktop/inputfile.txt';

open STDIN, '<', $data 
    or die "File error: input file: $!";
open STDOUT, '>', '/root/Desktop/output.log' 
    or die "File error: output file: $!";

my(%result) = ();

while (defined($_ = <STDIN>)) {
    chomp $_;
    my ($index, $value) = split( /\s/, $_, 0 );
    $result{$index} = $value;
}
while (my ($index, $value) = each(%result)) {
    do {
        say "$index => $value" if $value > 500;
    };
} 
close STDIN;
close STDOUT;
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Outputs:

5 => 550
[download]