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HACKY SOLUTION TO APPENDING AN "_" to ALL FILES IN PARENT DIRECTORY AND ITS CHILDREN
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1. Go to parent directory. Run the following line; it will generate a script file that you can run after to append an "_" before the file extension.

% find -iname '*.*' | while read f; do f=${f:2} ; echo mv \"$f\" \"${f/./_.}\"; done > rename.sh

2. Change permissions on your rename.sh file.

% chmod u+x rename.sh

3. Run in parent directory.

% ./rename.sh

4. Do note that you will get the following error:
% mv: cannot stat ‘’: No such file or directory

This is because you do not have an empty file with an empty name. Otherwise, everything should be a-ok.

NOTE: Your script file will also have an "_" appended too.