#!/bin/bash

OLD_TAG=$1
NEW_TAG=$2
FLAC=$3

# to change the name of a FLAC tag
# e.g., from MBZ_DISCID to MUSICBRAINZ_DISCID
metaflac --show-tag "$OLD_TAG" "$FLAC" \
    | sed "s/^$OLD_TAG=/$NEW_TAG=/" \
    | metaflac --remove-tag "$OLD_TAG" --import-tags-from - "$FLAC"