Finding duplicate files by name ignoring the case in subdirectories

find . -printf "%p %f\n" | sort -f -k2 | uniq -Di -f1

Specify your choice of starting directory for find if you don’t want to start at ..  Add -type f if you want just file names. 

• The find command produces a list of file (and directory) names, in directory order (i.e., random order, as far as you’re concerned).
• -printf "%p %f\n" prints the full pathname (relative to .) and the filename. 
• sort -f is short for sort --ignore-case, i.e., it sorts the filename list in a case-insensitive way
• -k2 tells it to use the second field as the sort key. 
• uniq -Di -f1 is short for uniq --all-repeated --ignore-case --skip-fields=1, i.e., it shows (all) the lines of output from find that occur repeatedly, based on case-insensitive comparison of the second field and beyond (i.e., that have the same (case-insensitive) file name).

This should give you the output that you want, except each line will have the filename repeated at the end.  If you want to get rid of that, pipe into sed 's/ .*//'.

A couple of gotchas:

• If you have directories whose names are the same except for case, and they contain files whose names are the same except for case, e.g.,

  documents/design.doc
  Documents/Design.doc
  

  then these will be listed.

• If you have files (or directories) whose names contain spaces, tabs, or newlines, this will break.

This works for basic file names, but will not work for files with carriage returns and probably a few other edge cases.

FilesNoPath=$(find . -printf "%f\n")
FilesWithPath=$(find .)

oldIFS=$IFS
IFS=$'\n'
for filename in $FilesNoPath;
do
    Matches=$(echo "$FilesWithPath" | grep -i "/$filename$")
    if [ $(echo "$Matches" | wc -l) -gt 1 ]
    then
        echo Found matches:
        echo "$Matches"
        FilesWithPath=$(echo "$FilesWithPath" | grep -vi "/$filename$")
    fi
done
IFS=$oldIFS

You can replace the . in the two find commands with /path/to/your/files if you want the output to show the full path and/or you don't want to execute this from within the parent directory of the matching files.