Rename all files in a folder from camel case to lowercase and put underscore to separate words

Question

I have a bunch of files like FileNameX.cpp and I would like to rename all of them to their respective file_name_x.cpp.

Answer 1

This bash command do the job. From the command line, enter the folder, and run this line:

for file in ./* ; do mv "$file" "$(echo $file|sed -e 's/\([A-Z]\)/_\L\1/g' -e 's/^.\/_//')" ; done

In script form it looks like this:

#!/bin/bash
for file in ./* ; do
    mv "$file" "$(echo $file|sed -e 's/\([A-Z]\)/_\L\1/g' -e 's/^.\/_//')"
done

Basically sed is used to manipulate strings. There're two expressions:

1. s/\([A-Z]\)/_\L\1/g: searches for capitals to substitutes them for lower case and add the underscore

2. s/^.\/_//: removes any underscore which was inserted due to the first letter being a capital (i.e. you don't want _file_name_x.cpp.

Consider using -v, --verbose on mv to explain what is being done.