my $str = 'sometrash key1=value0 value1, value2 key2=value3 key3=value4';

my @tokens;
for my $token (split(" ", $str)) {
    if ($token =~ m/=/) {
       push @tokens, $token; 
    } else {
        next unless @tokens;
        $tokens[-1] .= ' ' . $token;
    }
}

my %tokens = map { split("=", $_) } @tokens;