Network kanji filter: convert kanji code from one encoding to another. More information: https://manned.org/nkf.
nkf -w path/to/file.txt
nkf -s path/to/file.txt
nkf -w --overwrite path/to/file.txt
nkf -d --overwrite path/to/file.txt
nkf -c --overwrite path/to/file.txt
nkf -m --overwrite path/to/file.txt