Unicode normalization

NFD to NFC with convmv

 $ brew install convmv

 # Convert all files in a directory from NFD to NFC:
 $ convmv -f utf-8 -t utf-8 --nfc --notest .

 # Convert all files in a directory from NFC to NFD:
 $ convmv -f utf-8 -t utf-8 --nfd --notest .

NFD to NFC with iconv

 $ iconv -f UTF-8 -t UTF-8-MAC

NFD to NFC with rsync

 $ rsync --iconv=utf-8,utf-8-mac