In case you want to start using an array for the entry as soon as there is more than one element (and only then), you could do 

    ...
    my $key = <STDIN>;
    chomp($key);
    my $val = <STDIN>;
    chomp($val);
    if (exists $hash{$key}) {
        $hash{$key} = [ $hash{$key} ] unless ref($hash{$key});
        push @{$hash{$key}}, $val;
    } else {
        $hash{$key} = $val;
    }

[download]

Update: this would produce a data structure like this 

$VAR1 = {
          'bar' => 'val3',
          'baz' => 'val4',
          'foo' => [
                     'val1',
                     'val2'
                   ]
        };

[download]

Whether that's convenient to use further on, is another question... Maybe you'd want to always use an array for each entry, in which case you could simply write (using autovivification): 

    ...
    my $key = <STDIN>;
    chomp($key);
    my $val = <STDIN>;
    chomp($val);
    push @{$hash{$key}}, $val;

[download]

producing: 

$VAR1 = {
          'bar' => [
                     'val3'
                   ],
          'baz' => [
                     'val4'
                   ],
          'foo' => [
                     'val1',
                     'val2'
                   ]
        };

[download]

In reply to Re: Converting a hash element into an array by almut
in thread Converting a hash element into an array by rockers

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.