use warnings;
use strict;

my $input = "one 1 two 2 three 3 odd_element";

my $REGEX = qr{ \s* \b (\w+) \s+ (\w+) \b \s* }msx;
my %output;
pos($input)=undef;
while ($input=~/\G$REGEX/gc) {
	$output{$1} = $2;
}
my $rest = substr $input, pos $input;
if (length $rest) { # leftovers
	$output{$rest} = 'turkeysandwich';
}

use Data::Dumper;
print Dumper(\%output);
__END__
$VAR1 = {
          'one' => '1',
          'two' => '2',
          'three' => '3',
          'odd_element' => 'turkeysandwich'
        };