Hello, and welcome back! Are you ready for a new challenge? In this unit, we're stepping up a notch to tackle a complex yet intriguing task. It involves parsing complex strings into Ruby hashes and then updating them, a common requirement in many real-world tasks. So yes, this unit's session is going to be quite pragmatic — just the way you like it!

This task involves transforming a given string into a nested Ruby hash and updating a specific key-value pair within that hash. The input string will take the form "Key1=Value1,Key2=Value2,...". When a part of the value is another key-value string, we create a nested hash.

For example, the string "A1=B1,C1={D1=E1,F1=G1},I1=J1" should be transformed into the following nested hash:

Your Ruby function should parse this string into the above hash, then update the value of the nested key F1 from G1 to some other value, say 'NewValue'. The function should ultimately return the updated hash.

Our first step here will be to parse the string into a nested hash. Before diving into coding, let us understand that simple string splitting methods do not handle hierarchical structures well; hence, our solution needs to account for the nested nature of our text.

As you parse the string, you'll have to read through each character and note its role. Here's a hint: every time the = symbol is encountered, you can infer that the text bit you have on your hands is a key. Further, upon hitting the , symbol, you should gather that you've just finished reading a value. At this stage, it is safe to add the key-value pair you've just read into the hash you're constructing.

The next step calls for special attention to the braces. When you encounter an opening brace {, you should know you are taking a step deeper into the hierarchy. On the other hand, when you encounter a closing brace }, you are taking a step back up.

Now we have the parsed hash. We can move into the final phase of the task: updating a specific key-value pair. We will scour the hash for the specified key, which might be found at the base level or nested within another key's value. If it's a nested key-value pair, we would be updating the value within the nested hash. If it's a base-level key-value pair, the update will be in the base hash.

The final parse_string_and_update_value function pulls together all pieces of our solution. First, it parses the string, then it updates the requested key-value pair.

Well done! You've completed an intensive hands-on session dealing with complex strings and nested hashes in Ruby. This type of task often mirrors real-life scenarios, where you process complex data and make updates based on particular criteria.

Now it's your turn to reinforce what you've learned in this unit. Try practicing with different strings and attempt to update various key-value pairs. I'm confident that with practice, you'll be able to apply these coding strategies to a wide range of problems. Until our next learning adventure, happy coding!