lossless-compress

#!/bin/bash

readonly program="$(basename "${0}")"
readonly formats=('jpg' 'png' 'gif')

function depends_on {
  local -r all_deps=("${@}")
  local missing_deps=()

  for dep in "${all_deps[@]}"; do
    hash "${dep}" 2> /dev/null || missing_deps+=("${dep}")
  done

  if [[ "${#missing_deps[@]}" -gt 0 ]]; then
    echo 'Missing required tools:' >&2
    printf '  %s\n' "${missing_deps[@]}" >&2
    exit 1
  fi
}

function usage {
  echo "
    Losslessly compress files. Supported formats:
      ${formats[*]}

    Usage:
      ${program} <file...>

    Options:
      -h, --help   Show this help.
  " | sed -E 's/^ {4}//'
}

if [[ "${#}" -lt 1 ]]; then
  usage
  exit 1
fi

if [[ "${1}" =~ ^(-h|--help)$ ]]; then
  usage
  exit 0
fi

depends_on 'jpegtran' 'optipng' 'gifsicle'

for image_file in "${@}"; do
  echo "Compressing ${image_file}…"

  file_type="$(file --mime-type --brief "${image_file}" | cut -d'/' -f2)"

  if [[ "${file_type}" == 'jpeg' ]]; then
    jpegtran -copy none -optimize -progressive -outfile "${image_file}" "${image_file}"
  elif [[ "${file_type}" == 'png' ]]; then
    oxipng --quiet "${image_file}"
  elif [[ "${file_type}" == 'gif' ]]; then
    gifsicle --optimize=3 --batch "${image_file}"
  else
    echo "'${file_type}' is not a supported image type."
  fi
done