bash script to create all necessary sizes of app icons for Android applications

make-android-app-icons.sh

#!/bin/bash
#
# Given a source image, create icons in all sizes needed for an Android launcher icon.
#
# First (required) argument is path to source file.
#
# Second (optional) argument is the filename to be used for the output files.
# If not specified, defaults to "ic_launcher.png".
# 
# Third (optional) argument is path to the GraphicsMagick gm executable.
# If not specified, defaults to /usr/local/bin/gm.
#
# Requires GraphicsMagick. ("brew install graphicsmagick" on macOS)

set -e

if [ -z "$1" ]; then
    echo "usage: make-android-app-icons filename [output-file-name] [gm-path]"
    exit 1
fi

source_file=$1
output_file_name=ic_launcher.png
gm_path=/usr/local/bin/gm

if [ ! -z "$2" ]; then
    output_file_name=$2
fi

if [ ! -z "$3" ]; then
    gm_path=$3
fi

if [ ! -e "$gm_path" ]; then
    echo "error: GraphicsMagick executable not found at $gm_path"
    exit 1
fi

generate_size() {
    size=$1
    output_file=$2
    "$gm_path" convert "$source_file" -resize ${size}x${size}\! "$output_file"
}

/bin/mkdir -p ./mdpi
/bin/mkdir -p ./hdpi
/bin/mkdir -p ./xhdpi
/bin/mkdir -p ./xxhdpi
/bin/mkdir -p ./xxxhdpi
/bin/mkdir -p ./play_store

generate_size  48 "./mdpi/${output_file_name}"
generate_size  72 "./hdpi/${output_file_name}"
generate_size  96 "./xhdpi/${output_file_name}"
generate_size 144 "./xxhdpi/${output_file_name}"
generate_size 192 "./xxxhdpi/${output_file_name}"
generate_size 512 "./play_store/${output_file_name}"