Question

Now before you face palm and click on duplicate entry or the like, read on, this question is both Theory and practical.

From the title it is pretty obvious what I am trying to do, find some files, then rename them. Well the problem, there is so many way to do this, that I finally decided to pick one, and try to figure it out, theoretically.

Let me set the stage:
Lets say I have 100 files all named like this Image_200x200_nnn_AlphaChars.jpg, where the nnn is a incremental number and AlphaChars ie:

Image_200x200_001_BlueHat.jpg
Image_200x200_002_RedHat.jpg
...
Image_200x200_100_MyCat.jpg

Enter the stage find. Now with a simple one liner I can find all the image files in this directory.(Not sure how to do this case insensitive)

find . -type f -name "*.jpg"

Enter the stage rename. On it’s own, rename expect you to do the following:

rename <search> <replace> <haystack>

When I try to combine the two with -print0 and xargs and some regular expressions I get stuck, and I am almost sure it’s because rename is looking for the haystack or the search part… (Please do explain if you understand what happens after the pipe)

find . -type f -name "*.jpg" -print0 | xargs -0 rename "s/Image_200x200_(\d{3})/img/"

So the goal is to get the find to give rename the original image name, and replace everything before the last underscore with img

Yes I know that duplicates will give a problem, and yes I know that spaces in the name will also make my life hell, and don’t even start with sub directories and the like. To keep it simple, we are talking about a single directory, and all filename are unique and without special characters.

I need to understand the fundamental basics, before getting to the hardcore stuff. Anybody out there feel like helping?

Answer 1

Another approach is to avoid using rename — bash is capable enough:

find ... -print0 | while read -r -d '' filename; do
  mv "$filename" "img_${filename##*_}"
done

the ##*_ part remove all leading characters up to and including the last underscore from the value.