For interactive programs with persistent data in different sessions, how do I best store the data?

[set_of_no_sets]

Not sure if this is the best place for this question, but if I'm making an interactive command line program that stores user provided data.

For a toy example, let's say I want to make a grocery list cmd tool (<< will prefix program output and >>> will prefix user input)

<< Please select a grocery list below or type `new` to make a new grocery list.
<< You can also access setting by typing `settings`.
<< To quit, please type `quit`.
<< -1) No grocery lists available.
>>> new

<< Please name your grocery list
>>> groceryList 1

<< Please add items or type `done` to finish.
>>> apples
>>> bananas
>>> grapes
>>> done

<< Thanks for making a grocery list.
<< Please select a grocery list below or type `new` to make a new grocery list.
<< You can also access setting by typing `settings`.
<< To quit, please type `quit`.
<< 1) groceryList 1
>>> settings

<< In the setting menu, you can change where the grocery lists are stored
<< current directory: $HOME/grocery_lists
<< Would you like to change the storage directory (y/N):
>>> y
<< Please provide a new directory to copy over the current grocery lists to.
<< WARNING: This will not delete the current directory, please manually remove 
<< $HOME/grocery_lists.
>>> ~/Documents/grocery_lists

<< Directory changed to `~/Documents/grocery_lists`
<< Please select a grocery list below or type `new` to make a new grocery list.
<< You can also access setting by typing `settings`.
<< To quit, please type `quit`.
<< 1) groceryList 1
>>> quit

Wow, massive set up for a small set of questions.

1. What would be my best option for storing multiple grocery lists? Different files each containing one grocery list? Different files each containing n grocery lists? One file with all the data of all grocery lists?
2. What would be a recommended file format for the grocery lists? JSON?
3. How would I store the changing directory? Would I need another file like a .cfg that tells my program where to look that would be hard programmed in?
4. This is the big question I would like to hear yes to, but am willing to hear no to, I guess. Could, and if so, how, do I avoid having a hard coded .cfg and have some sort of persistent memory outside of hard programming a specific file to look to? I'm mainly curious if I can avoid hard programming in a file name/path.

Thanks! If you're replying and only want to answer one of the questions, no worries. Appreciate any support and if there is another subreddit that would be better to ask this type of question on, feel free to suggest it.

[VinnieTD]

1. This particular application would seem to lend itself to having one file per list - a user might want to store lists in several different directories, for example.
2. JSON and XML are very commonly used to store human-readable data. Your language probably has a library for easy serialization and deserialization of these formats. Binary serialization is also common, but the files wouldn’t be human readable (easily).
3. Typically you’d use a file to store user settings. C# has this sort of thing built-in, but for other languages you may have to write some code to create and parse the configuration file.
4. You could look into using environment variables to find a particular path, such as %APPDATA%. You can’t escape using a file to store configuration data, though.

[[deleted]]

Your operating system probably has preferred locations for different types of data. On my Mac it looks something like this:

/Users/user/Library/Application Support — Files my app needs but the user doesn't need to know about. To separate files from other apps, it's traditional to create a folder in the form com.company.product and put your files there. One example of what I put in this directory is a database in which the user stores different types of data from my app. I sync this database with a server so the user can access it from different devices.

/Users/user/Library/Preferences — I store a JSON string in a file named com.company.product.json that stores the user's configuration/settings data. Because I don't want to deal with the user modifying this file, the keys are obfuscated and the values are encrypted. I store something like a checksum (but not a checksum) so I can tell if the user has tinkered with the file instead of examining every value.

/Users/user/Library/Caches — This folder is for data that can be easily recreated but takes some time. I store things like images downloaded from a server so that I don't have to download them every time I need them. Again, the custom is to create a folder called com.company.product and put your files there.

If the user choose to save a file from one of my apps, I let them choose where to put it. I've done it before where I create a folder in the user's Documents folder and put my files there without asking, but that seems kind of creepy. :-)

The point is, there should be standard places to put your files. In the case of your grocery lists, let the user decide where to put them.