An utility to add BOM to UTF-8 files

addbom

#!/usr/bin/env bash

set -e

if [[ $# == 1 ]]; then
	INPUT="$1"
	OUTPUT="$(mktemp)"
	SUCCESS=0
	function commit
	{
		if [[ "$SUCCESS" == "1" ]]; then
			mv "$OUTPUT" "$INPUT"
		fi
		rm -f "$OUTPUT"
	}
	trap commit EXIT
	FAIL_IF_OUTPUT_EXISTS=0
elif [[ $# == 2 ]]; then
	INPUT="$1"
	OUTPUT="$2"
	FAIL_IF_OUTPUT_EXISTS=1
else
cat << ENDSYNTAX
Adds a byte order mark to a file and converts to UTF-8
https://gist.github.com/chanibal/397c39d59ede8682ce13

Syntax:
addbom file_to_add_byte_order_mark
addbom input_file output_file
ENDSYNTAX
	exit 0
fi

if [[ ! -e "$INPUT" ]]; then
	echo "Error: no file: $INPUT"
	exit 1;
fi

read -n 3 MAGIC <"$OUTPUT"
if [[ "$MAGIC" == $(echo -ne '\xEF\xBB\xBF') ]]; then
	echo "Error: $OUTPUT already has bom"
	exit 2
fi

(echo -ne '\xEF\xBB\xBF' && iconv -t utf-32 | iconv -f utf-32 -t utf-8) <"$INPUT" >"$OUTPUT"
SUCCESS=1