Understanding the sed command - bash

Question

I'm trying to change every first line in all files contained in a parent directory so that they inherit the pathname of the directory that they're in.
For example I have a file with the format:
2000-01-18
Tuesday
Livingston
42178
This particular file is in a directory named 18, inside another directory named 01, which is in another directory named 2000, which is in a directory called filesToSort.
I managed to use this code as a console command to change the first line of the file:
perl -pi -w -e 's/2000-01-18/Test/g;' ff_1177818640
This changed the file to
Test
Tuesday
Livingston
42178
Is it possible for me to change the "date" in this command to select all dates, I tried to use it like this:
perl -pi -w -e 's/*/Test/g;' ff_1177818640
But it didn't like that at all.
My current though process is that if I can make this command select all dates in the initial input, then some how find a way to implement the pathname into the second part where I currently have "Test" using something like this:
path=/filesToSort/2000/01/18/ff_1177818640
file=$(basename "$path")
I should in theory be able to run this entire code through my parent directory and all sub directories, therefore changing every date value in the files, which apear on line 1 of every single file, in these directories to mirror the file path that they're in, effectively turning a file that looks like this:
2000-xx-18
Tuesday
Livingston
42178
Contained in directory /filesToSort/2000/01/18
into this:
2000/01/18
Tuesday
Livingston
42178
I'm not sure if I'm just using the sed command wrong here and that there is another command that I should be using instead but I've been trying to get this to work for 4 hours now and I can't seem to nail it.
Thanks in advance for the help!

Answer 1

Looks to me that what you want to do is basically translate "-" for "/". You could, find the file, take a backup of it (always a good idea) and then use :
sed 's|-|/|g' <path/backup_file >path/modified_file
That said, if it is the same assignement, you could use that command to copy to its new directory and modified the file at the same time.

Answer 2

You haven't posted a sed command, so it's hard to know what will work. Let's take this in small steps. Try this:
sed -i '1s/^/X/' ff_1177818640
and see if that modifies the file (adding 'X' to the beginning of the first line). If your version of sed doesn't like that, try this:
sed -i "" '1s/^/X/' ff_1177818640
Once you have the syntax working, we must tackle the problem of converting a path into a date. Try this:
echo some/path/filesToSort/2000/01/18/ff_1177818640 | sed 's|.*/filesToSort/||; s|/[^/]*$||'
If that produces "2000/01/18", post a comment, and we can put it all together.
EDIT: putting it all together. Abracadabra!
find . -type f -exec sed -i "1{s|.*|{}|;s|.*/filesToSort/||;s|/[^/]*$||;}" {} \;