#!/bin/bash

# Tag line editing
# Change the line
# from
#     vocabulary grammar
# to
#    tag:: vocabulary grammar
# Change by given tag value such as "vocabulary" or "grammar"
# Omit the tag line if they already have the key word of "tag"
# Backup your data first if they're important

data_dir=/path/to/data_dir

tagvalue="vocabulary"

tagline_filter="/^tag/!"
tagkey="tag:: "
filtered_operation="s/^\(.*$tagvalue\([[:space:]]\|$\)\)/$tagkey\1/"
sed_directive="$tagline_filter $filtered_operation"
echo "$sed_directive"

find_cmd="find $data_dir -maxdepth 1 -type f"

for fpath in `$find_cmd`
do
    echo $fpath
    sed -e "$sed_directive" -i $fpath
done