A bash script to rename files from different directories at once - bash

Question

If I have a directory named /all_images, and inside this directory there's a ton of directories, all the directories named dish_num as shown below. and inside each dish directory, there's one image named rgb.png. How can i rename all the image files to be the name of its directory.
Before
|
├── dish_1
│ └── rgb.png
├── dish_2
│ └── rgb.png
├── dish_3
│ └── rgb.png
├── dish_4
│ └── rgb.png
└── dish_5
└── rgb.png
After
|
├── dish_1
│ └── dish_1.png
├── dish_2
│ └── dish_2.png
├── dish_3
│ └── dish_3.png
├── dish_4
│ └── dish_4.png
└── dish_5
└── dish_5.png

Answer 1

WARNING: Make sure you have backups before running code you got someplace on the Internet!
find /all_images -name rgb.png -execdir sh -c 'mv rgb.png $(basename $PWD).png' \;
where
find /all_images will start looking from the directory "/all_images"
-name rbg.png will look anywhere for anything named "rbg.png"
optionally use -type f to restrict results to only files
-exedir in every directory where you got a hit, execute the following:
sh -c shell script
mv move, or "rename" in this case
rgb.png file named "rgb.png"
$(basename $PWD).png output of "basename $PWD", which is the last section of the $PWD - the current directory - and append ".png" to it
\; terminating string for the find loop

Answer 2

If you want to benefited from your multi-core processors, consider using xargs instead of find -execdir to process files concurrently.
Here is a solution composed of find, xargs, mv, basename and dirname.
find all_images -type f -name rgb.png |
xargs -P0 -I# sh -c 'mv # $(dirname #)/$(basename $(dirname #)).png'
find all_images -type f -name rgb.png prints a list of file paths whose filename is exactly rgb.png.
xargs -P0 -I# CMD... executes CMD in a parallel mode with # replaced by path names from find command. Please refer to man xargs for more information.
-P maxprocs
Parallel mode: run at most maxprocs invocations of utility at once. If maxprocs is set to 0, xargs will run as many processes as possible.
dirname all_images/dash_4/rgb.png becomes all_images/dash_4
basename all_images/dash_4 becomes dash_4
Demo
mkdir all_images && seq 5 |
xargs -I# sh -c 'mkdir all_images/dash_# && touch all_images/dash_#/rgb.png'
tree
find all_images -type f -name rgb.png |
xargs -P0 -I# sh -c 'mv # $(dirname #)/$(basename $(dirname #)).png'
tree
Output
.
└── all_images
├── dash_1
│   └── rgb.png
├── dash_2
│   └── rgb.png
├── dash_3
│   └── rgb.png
├── dash_4
│   └── rgb.png
└── dash_5
└── rgb.png
.
└── all_images
├── dash_1
│   └── dash_1.png
├── dash_2
│   └── dash_2.png
├── dash_3
│   └── dash_3.png
├── dash_4
│   └── dash_4.png
└── dash_5
└── dash_5.png
6 directories, 5 files