Regex and shell - multiple recursive rename - regex

Question

I have a folder with several hundreds of folders inside it. These folders contain another folder each, called images, and in this folder there is sometimes a strictly numerically named .jpg file. Sometimes there are other JPG files in the folder as well, but these need to be ignored if they aren't strictly numeric.
I would like to learn how to write a script which would, when run in a given folder, traverse every single subfolder and look for this numeric file. It would then add the "_n" suffix to a copy of each, if such a file does not already exist.
Can this be done through the unix terminal easily?
To be more specific, this is the structure I'm dealing with:
master folder
18556
images
2234.jpg
47772
images
2234.jpg
2234_n.jpg
some_pic.jpg
77377
images
88723
images
22.jpg
some_pic.jpg
After the script is run, the situation would look like this:
master folder
18556
images
2234.jpg
2234_n.jpg
47772
images
2234.jpg
2234_n.jpg
some_pic.jpg
77377
images
88723
images
22.jpg
22_n.jpg
some_pic.jpg
Update: Sorry about the typo, I accidentally put 2235 into 47772.
Update 2: Regarding the 2nd comment on the mathematical.coffee's answer, the OS I am currently on (at work) is MacOS, but my main machines are running CentOS and Ubuntu at home, so I just assumed my situation applies to all unix based systems.

Answer 1

You can use the -regex switch to find to match /somefolder/images/numeric.jpg:
find -type f -regex './[^/]+/images/[0-9]+\.jpg$'
Edit: refinement from #JonathanLeffler: add -type f to find so it only finds files (ie don't match a directory called '12345.jpg').
The ./[^/]+/ is for the first folder (if that first folder is always numeric too you can change it to [0-9]+).
The [0-9]+\.jpg$ means a jpg file with file name only being numeric.
You might want to change the jpg to jpe?g to allow .jpeg, but that's up to you.
Then it's a matter of copying these to xxx_n.jpg.
for f in $(find -type f -regex './[^/]+/images/[0-9]+\.jpg$')
do
# replace '.jpg' in $f (filename) with '_n.jpg'
newf=${f/\.jpg/_n\.jpg}
# see if this new file exists
if [ ! -f $newf ];
then
# if not exists, copy it.
cp "$f" "$newf"
fi
done

Answer 2

What should be the logic behind the renames in Folder 47772? If we assume you want to rename all the files just consisting of numbers to numbers + _n
With mmv you could write it like:
mmv "[0-9][0-9]*.jpg" "#1#2#3_n.jpg"
Note: mmv is for moving; mcp is for copying, and so is more appropriate to this question.
Question of Vader:
Well I checked the man page and the problem is that it's a bit strange.
I was thinking [0-9]* would match zero or more numbers. I turns out that this assumption was wrong.
The problem is that I could not tell I want two or more numbers at the start of the name.
So [0-9][0-9]* matches a name starting with at least two numbers (after that it takes all the rest up to the .. Now every [0-9] is one pattern and so I had to make the to pattern into:
"#1#2#3_n.jpg" With e.g 1234.jpg I have #1 = 1; #2 = 2, #3 = 34 So
#1#2#3 -> 1234; _n appends the _n and .jpg the extension
However it would rename also files with 12some_other_stuff.jpg sot 12some_other_stuff_n.jpg. It's not ideal but achieves in this context what was intended.