Simple bash script to prepare images for the web

$ identify images/cheat-cube.png
images/cheat-cube.png PNG 1024x724 1024x724+0+0 8-bit sRGB 403KB 0.000u 0:00.000

#!/bin/bash

# Define the usage text.
USAGE=$( cat <<EOF
Usage: `basename $0` [-hvd] [-W <max_width>] [-H <max_height>] [-c <target-format>] [-o <output-directory>] [-q <quality>\n
-h|--help:
\tDisplays this help.
-v|--version
\tDisplays the current version of this script.
-W|--max-width
\tMaximum image width.
-H|--max-height
\tMaximum image height.
-c|--convert
\tFormat the image gets converted to.
-o|--output-directory
\tDirectory to save the new files to.
-q|--quality
\tQuality of the newly generated image (value between 0 and 100).
EOF
)

# Declare all used variables.
MAX_WIDTH=""
MAX_HEIGHT=""
CONVERT=""
QUALITY=""
OUTPUT_DIR=""

# Functions for messages.
function notice() {
  echo -e "$*" >&2
}

function info() {
  echo -e "$*" >&2
  exit 0
}

function error() {
  echo -e "$*" >&2
  exit 1
}

# Check if a given program is installed.
haveProg() {
  which $1 &> /dev/null
}

# Join array to string.
join() {                                                                        
  local IFS="$1"
  shift
  echo "$*"
}

# Declare a list of packages needed in order to use this script.
packages=('convert' 'identify')

# Generate a list of missing packages.
missing=()
cnt=${#packages[@]}
for ((i=0;i<cnt;i++)); do
  if ! haveProg "${packages[i]}"; then
    missing+=("${packages[i]}")
  fi
done

# Dump an error message for missing packages.
if [[ ${#missing[@]} -ne 0 ]] ; then
  missingStr=`join ' ' ${missing[@]}`
  error "The following packages are missing: $missingStr"
fi

# Initialize the positional argument list ...
args=()

# ... and fetch command line options.
while [[ -n "${1+xxx}" ]]; do
  case "$1" in
    --help|-h)
      info "$USAGE"
      ;;
    --version|-v)
      info "`basename $0` version 1.0"
      ;;
    --max-width|-W)
      shift
      MAX_WIDTH=$1

      re='^[0-9]+$'
      if ! [[ $MAX_WIDTH =~ $re ]] ; then
        error "Given max width is not a number."
      fi
      shift
      ;;
    --max-height|-H)
      shift
      MAX_HEIGHT=$1

      re='^[0-9]+$'
      if ! [[ $MAX_HEIGHT =~ $re ]] ; then
        error "Given max height is not a number."
      fi
      shift
      ;;
    --convert|-c)
      shift
      CONVERT=$1
      
      if ! [[ "$CONVERT" ]] ; then
        error "Missing target format to convert to."
      fi

      CONVERT=$(tr '[:upper:]' '[:lower:]' <<< $CONVERT)

      shift
      ;;
    --output-directory|-o)
      shift
      OUTPUT_DIR=${1%/}
      
      if [ -z "$OUTPUT_DIR" ] || [ ! -d "$OUTPUT_DIR" ] ; then
        error "Missing or not existing output directory."
      fi

      shift
      ;;
    --quality|-q)
      shift
      QUALITY=$1

      re='^(100|[1-9][0-9]|[0-9])$'
      if ! [[ $QUALITY =~ $re ]] ; then
        error "Given quality is not valid."
      fi
      shift
      ;;
    -*)
      error "unrecognized option: $1\n\n$USAGE"
      ;;
    *)
      args+=("$1")
      shift
      ;;
  esac
done

cnt=${#args[@]}
for ((i=0;i<cnt;i++)); do
  file="${args[i]}"

  # Extract the image dimensions from the info blob ...
  identity=`identify $file | awk '{print $3}'`

  # ... and split dimensions to width and height.
  dimensions=(${identity//x/ })
  width=${dimensions[0]}
  height=${dimensions[1]}

  # Extract the path, filename, basename and extension.
  filename=$(basename "$file")
  extension="${filename##*.}"
  filename="${filename%.*}"
  path=$(dirname "$file")

  # Set target directory.
  outDir="$path"
  if [ ! -z "$OUTPUT_DIR" ]; then
    outDir="$OUTPUT_DIR"
  fi

  # Identify the current file.
  printf '\n-> %s (%s x % s) %s\n' "$file" "$width" "$height" "$extension"
  
  # Generate the new filename.
  newFile=$(printf '%s/%s.%s' "$outDir" "$filename" "$CONVERT")

  # Convert the file if needed.
  if [ ! -z "$CONVERT" ] && [ "$extension" != "$CONVERT" ]; then
    printf 'Converting %s to %s\n' "$file" "$newFile"
    convert "$file" "$newFile"
  fi

  if [ ! -f "$newFile" ]; then
    cp "$file" "$newFile"
  fi

  # Scale down the image in width if needed.
  if [ ! -z "$MAX_WIDTH" ] && [ "${width:-0}" -ge "${MAX_WIDTH}" ]; then
    printf 'Scaling image down from a width of %s pixels to %s pixels.\n' "$width" "$MAX_WIDTH"
    convert "$newFile" -resize "$MAX_WIDTH" "$newFile"

    # Extract the image dimensions from the info blob ...
    identity=`identify $newFile | awk '{print $3}'`

    # ... and split dimensions to width and height.
    dimensions=(${identity//x/ })
    width=${dimensions[0]}
    height=${dimensions[1]}
  fi

  # Scale down the image in height if needed.
  if [ ! -z "$MAX_HEIGHT" ] && [ "${height:-0}" -ge "${MAX_HEIGHT}" ]; then
    printf 'Scaling image down from a height of %s pixels to %s pixels.\n' "$height" "$MAX_HEIGHT"
    convert "$newFile" -resize "x$MAX_HEIGHT" "$newFile"
  fi

  # Reduce the quality of the image if needed.
  if [ ! -z "$QUALITY" ]; then
    printf 'Reducing the image quality to %s percent\n' "$QUALITY"
    convert "$newFile" -quality "$QUALITY" "$newFile"
  fi
done

$ identify images/cheat-cube.jpg
images/cheat-cube.jpg JPEG 565x400 565x400+0+0 8-bit sRGB 40.9KB 0.000u 0:00.000