You said, ...push multiple key-value pairs onto an existing hash. Just to clarify, values (scalars) are pushed onto an array; you don't push onto a hash.

The push in your while loop adds array references as values associated with keys, so you see a mix of data from the Dumper output (your push @{$gene{$key}}, $value; notation says treat the key's associated value as an array and push the contents of $value onto that array):

$VAR1 = {
          'HES4' => '57801',
          'TMEM52' => [
                        '339456'
                      ],
          'SSU72' => [
                       '29101'
                     ],
          'GNB1' => [
                      '2782'
                    ],
          'PLEKHN1' => '84069',
          'NCRNA00115' => '79854',
          'ATAD3A' => [
                        '55210'
                      ],
          'ATAD3B' => [
                        '83858'
                      ],
          'SLC35E2' => [
                         '9906'
                       ],
          'SAMD11' => '148398',
          'NOC2L' => '26155'
        };

[download]

The [ ] notation indicates a list--each one having been generated by the push--so your hash now contains array references and non-reference values.

choroba has shown you how to add the key-value pairs to an existing hash (which will overwrite an existing value, if the key already exsits):

while(<DATA>){
    chomp;
    my ($key, $value) = split;
    $gene{$key} = $value; # choroba's suggestion
}

[download]

Dumper output:

$VAR1 = {
          'HES4' => '57801',
          'TMEM52' => '339456',
          'SSU72' => '29101',
          'GNB1' => '2782',
          'PLEKHN1' => '84069',
          'NCRNA00115' => '79854',
          'ATAD3A' => '55210',
          'ATAD3B' => '83858',
          'SLC35E2' => '9906',
          'SAMD11' => '148398',
          'NOC2L' => '26155'
        };

[download]

Is this what you wanted to achieve?

In reply to Re^3: pushing multiple key-value pairs into an existing hash by Kenosis
in thread pushing multiple key-value pairs into an existing hash by lomSpace

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.