base16

#!/usr/bin/env bash
#
# base16
#
# Base16 encode/decode data.
#
# Author: Emanuel Duss
#

set -o errexit
set -o nounset
set -o pipefail

print_usage(){
cat << EOI
Usage: base16 [OPTION]... [FILE]
Base16 (Hex) encode or decode FILE, or standard input, to standard output.
With no FILE, or when FILE is -, read standard input.

Options:
  -d         decode data
  -i         when decoding, ignore non-alphabet characters
  -w COLS    wrap encoded lines after COLS character (default 76).
             Use 0 to disable line wrapping

  -h         display this help and exit

The data are encoded as described for the base16 alphabet in RFC 4648.
When decoding, the input may contain newlines in addition to the bytes of
the formal base64 alphabet.  Use -i to attempt to recover from any other
non-alphabet bytes in the encoded stream.
EOI
}

check_dependencies(){
  local FAIL=0
  local MISSING=""
  for tool in $@
  do
    if ! hash "$tool" &> /dev/null
    then
      MISSING="$MISSING, $tool"
      FAIL=1
    fi
  done
  if [[ "$FAIL" == 1 ]]
  then
    echo "Missing dependency: ${MISSING/, }."
    exit 1
  fi
}

parse_arguments(){
  WRAP_COLS="76"
  while getopts diw:h name
  do
    case $name
    in
      d)
        DECODE="1"
      ;;
      i)
        IGNORE_GARBAGE="1"
      ;;
      w)
        WRAP="1"
        WRAP_COLS="$OPTARG"
      ;;
      h)
        print_usage
        exit
      ;;
      ?)
        print_usage >&2
        exit 1
      ;;
    esac
  done
}

hex_to_binary(){
  perl -e '
    local $/;
    $i = <>;
    $i =~ s/[\r\n]//g;
    if ($i =~ /[^0-9a-fA-F]/){
      print STDERR "base16: invalid input\n";
      exit 1;
    }
    print pack "H*", $i;'
}

hex_to_binary_ignore_garbage(){
  perl -e '
    local $/;
    $i = <>;
    $i =~ s/[^0-9a-fA-F\n\r]//g;
    print pack "H*", $i'
}

binary_to_hex(){
  # hexdump -ve '1/1 "%.2x"'
  perl -e '
    local $/;
    print unpack "H*", <>'
}

main(){
  check_dependencies perl

  parse_arguments "$@"
  shift $(($OPTIND - 1))

  # Only one file is allowed
  if [[ "$#" > 1 ]]
  then
    echo -e "base16: extra operand '$1'"
    echo "Try 'base16 -h for more information."
    exit 1
  fi

  # Use STDIN (-) if $1 is not set
  FILE="${1:--}"

  # Decode
  if [[ -n "${DECODE:-}" ]]
  then
    if [[ -n "${IGNORE_GARBAGE:-}" ]]
    then
      cat "$FILE" | hex_to_binary_ignore_garbage
    else
      cat "$FILE" | hex_to_binary
    fi
  # Encode
  else
    if [[ "$WRAP_COLS" == "0" ]]
    then
      cat "$FILE" | binary_to_hex | tr -d '\n'
    else
      cat "$FILE" | binary_to_hex | fold -w "$WRAP_COLS"
      echo # Print newline at the end
    fi
  fi

}

main "$@"