Possibly a little incorrect English ahead:
There are at least 2 folders. For this, A contains files without extension, usually usernames, and B contains similar files, with '.yml' extension or possibly without extension, or even other extension, that's not always the case.
How to find out if the files in the A folder exist in B, possibly under a different extension, without using scripting language such as Python ? It'd not be much of an issue for me to make a Python script, but for portability I'd prefer shell scripting, which I suck at. Not to mention I don't know all the commands.
It's only good if this can be done in non-Linux systems too, particularly BSD.
EDIT 0: The difference in name isn't always just the extension, the name could have characters before or after the same text. For example, if A had a file called
foobar, it could be named
location_foobar in B. Otherwise the name wouldn't be more different, like
foo1bar, that's entirely different thing, so the script wouldn't be looking for such differences.