bom-add

#!/usr/bin/env bash

# MIT License
#
# Copyright (c) 2023 John Karahalis
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

# Use "strict mode."
#
# http://redsymbol.net/articles/unofficial-bash-strict-mode/
set -euo pipefail

COMMAND_NAME=$(basename "$0")

eval "$(docopts --help=- -A ARGS : "$@" <<EOF
Add a byte order mark (BOM) to the beginning of input. If one is already
present, a second will not be added.

Usage:
  $COMMAND_NAME [FILE]
  $COMMAND_NAME -h | --help

Examples:
  $COMMAND_NAME example.csv
  (cat example.csv | $COMMAND_NAME) > example_with_bom.csv

Options:
  -h, --help
      Show this documentation
EOF
)"

# https://stackoverflow.com/a/35807131/715866
SED_EXPRESSION='1s/^\(\xef\xbb\xbf\)\?/\xef\xbb\xbf/'

if [[ ${ARGS[FILE]} ]]; then
  sed -i "$SED_EXPRESSION" "${ARGS[FILE]}"
else
  sed "$SED_EXPRESSION"
fi