How about this:

#!/usr/bin/perl -w
###############################################################
use strict;
use Data::Dumper;

my $data=qq(key1=value1 key2=value2 key3=value3 key4=value4);
my $v={};

foreach my $pair (split(' ',$data)) {
  my($key,$value)=split('=',$pair);
  $v->{$key}=$value;
}

print Dumper($v);
[download]

Yields:

$VAR1 = {
          'key1' => 'value1',
          'key2' => 'value2',
          'key3' => 'value3',
          'key4' => 'value4'
        };
[download]

Alternatively you can do the following with the same results

#!/usr/bin/perl -w
###############################################################
use strict;
use Data::Dumper;

my $data=qq(key1=value1 key2=value2 key3=value3 key4=value4);
my $v={};

map { my($k,$vl) = split('=',$_); 
      $v->{$k}=$vl;
    } split(' ',$data);

print Dumper($v);
[download]

HTH