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;
    }
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Update: this would produce a data structure like this

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

$VAR1 = {
          'bar' => [
                     'val3'
                   ],
          'baz' => [
                     'val4'
                   ],
          'foo' => [
                     'val1',
                     'val2'
                   ]
        };
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use strict;
use warnings;
sub getHash
{
  my %hash;
  for(my $i=0;$i<4;$i++)
  {
    my $key = <STDIN>;
    chomp($key);
    my $val = <STDIN>;
    chomp($val);

    if ( !defined $hash{$key} ) #first time
    {
        $hash{$key} = $val;
    }
    else
    {
        $hash{key} = ref($hash{key}) ? [ @{$hash{key}}, $val ] : [ $ha
+sh{key}, $val ];
    }
  }
}
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use strict;
use warnings;
sub getHash
{
  my %hash;
  for(my $i=0;$i<4;$i++)
  {
    my $key = <STDIN>;
    chomp($key);
    my $val = <STDIN>;
    chomp($val);

    push @{$hash{key}}, $val;
  }
}
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However, I need to maintain the distinction of scalar and array for different inputs. So, the first code really suites me! :)
Thanks again!

You can also distinguish that by looking at the number of elements of the array.


holli, /regexed monk/

my $key = <STDIN>;
chomp($key);
$hash{$key} = [] unless $hash{$key};
my $val = <STDIN>;
chomp($val);
push @{$hash{$key}}, $val;
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@luckypower and @holli:
Thanks, I was wrong. Declaring it as an array apriori is better.

for (0..3) {
   chomp(my $key = <STDIN>);
   chomp(my $val = <STDIN>);
   push @{$hash{$key}}, $val;
}
[download]

Entering 4 pairs this way is uncomfortable and error prone (forget to enter one item or press return twice and you have keys and values switched). If (for example) '=' can't occur in any key, entering them as 'key = value' might be better:

    my $all = <STDIN>;
    chomp($all);
    if ($all=~/([^=]+?)\s*=\s*(.*)/) {
      $hash{$1} = $2;
    }
    else {
      print "Input Error. \n";
      $i--;
    }
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  var query_string = {};
  var query = window.location.search.substring(1);
  var vars = query.split("&");
  for (var i=0;i<vars.length;i++) {
    var pair = vars[i].split("=");
        // If first entry with this name
    if (typeof query_string[pair[0]] === "undefined") {
      query_string[pair[0]] = pair[1];
        // If second entry with this name
    } else if (typeof query_string[pair[0]] === "string") {
      var arr = [ query_string[pair[0]], pair[1] ];
      query_string[pair[0]] = arr;
        // If third or later entry with this name
    } else {
      query_string[pair[0]].push(pair[1]);
    }
  }
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