Create iOS application icons from one PDF file. Requires ImageMagick.

Iconizer.sh

#!/bin/sh

#
# Iconizer shell script by Steve Richey (srichey@floatlearning.com)
# Modified by Rich Ellis (rich@richellis.net) based on contributions on Github from crishoj, giria
# https://gist.github.com/steverichey/8493f3bd31ae71a9c933/forks
#
# This is a simple tool to generate all necessary app icon sizes and the JSON file for an *EXISTING* Xcode project from one file.
# To use: specify the path to your vector graphic (PDF format) and the path to your Xcode folder containing Images.xcassets
# Example: sh iconizer.sh MyVectorGraphic.pdf MyXcodeProject
#
# Requires ImageMagick: http://www.imagemagick.org/
# Requires GhostScript: http://www.ghostscript.com/
#
# Install dependencies with Homebrew: http://brew.sh/
#    brew install imagemagic
#    brew install ghostscript

# Exit on first error
set -e

if [ $# -ne 2 ]
  then
        echo "\nUsage: sh iconizer.sh file.pdf FolderName\n"
elif [ ! -e "$1" ]
    then
        echo "Did not find file $1, expected path to a vector image file.\n"
elif [ ${1: -4} != ".pdf" ]
    then
        echo "File $1 is not a vector image file! Expected PDF file.\n"
elif [ ! -d "./$2/Images.xcassets/AppIcon.appiconset/" ]
    then
        echo "Did not find Xcode folder $2, expected folder which contains Images.xcassets/AppIcon.appiconset/ \n"
elif [ ! -x "$(command -v convert)" ]
    then
        echo "Executable 'convert' not found in path. Please install ImageMagick."
elif [ ! -x "$(command -v gs)" ]
    then
        echo "Executable 'gs' not found in path. Please install GhostScript."
else
    echo "Creating icons from $1 into $2/Images.xcassets/AppIcon.appiconset/..."

    for i in 16 29 32 40 50 57 58 64 72 76 80 87 100 114 120 128 144 152 167 180 256 512 1024
        do
            echo "Creating $i px icon"
            convert -density 400 $1 -scale $ix$i ./$2/Images.xcassets/AppIcon.appiconset/appicon_$i.png
    done

    echo "Created app icon files, writing Contents.json file..."

    echo '{"images":[
{\n"size":"29x29",\n"idiom":"iphone",\n"filename":"appicon_29.png",\n"scale":"1x"\n},
{\n"size":"29x29",\n"idiom":"iphone",\n"filename":"appicon_58.png",\n"scale":"2x"\n},
{\n"size":"29x29",\n"idiom":"iphone",\n"filename":"appicon_87.png",\n"scale":"3x"\n},
{\n"size":"40x40",\n"idiom":"iphone",\n"filename":"appicon_80.png",\n"scale":"2x"\n},
{\n"size":"40x40",\n"idiom":"iphone",\n"filename":"appicon_120.png",\n"scale":"3x"\n},
{\n"size":"57x57",\n"idiom":"iphone",\n"filename":"appicon_57.png",\n"scale":"1x"\n},
{\n"size":"57x57",\n"idiom":"iphone",\n"filename":"appicon_114.png",\n"scale":"2x"\n},
{\n"size":"60x60",\n"idiom":"iphone",\n"filename":"appicon_120.png",\n"scale":"2x"\n},
{\n"size":"60x60",\n"idiom":"iphone",\n"filename":"appicon_180.png",\n"scale":"3x"\n},
{\n"size":"29x29",\n"idiom":"ipad",\n"filename":"appicon_29.png",\n"scale":"1x"\n},
{\n"size":"29x29",\n"idiom":"ipad",\n"filename":"appicon_58.png",\n"scale":"2x"\n},
{\n"size":"40x40",\n"idiom":"ipad",\n"filename":"appicon_40.png",\n"scale":"1x"\n},
{\n"size":"40x40",\n"idiom":"ipad",\n"filename":"appicon_80.png",\n"scale":"2x"\n},
{\n"size":"50x50",\n"idiom":"ipad",\n"filename":"appicon_50.png",\n"scale":"1x"\n},
{\n"size":"50x50",\n"idiom":"ipad",\n"filename":"appicon_100.png",\n"scale":"2x"\n},
{\n"size":"72x72",\n"idiom":"ipad",\n"filename":"appicon_72.png",\n"scale":"1x"\n},
{\n"size":"72x72",\n"idiom":"ipad",\n"filename":"appicon_144.png",\n"scale":"2x"\n},
{\n"size":"76x76",\n"idiom":"ipad",\n"filename":"appicon_76.png",\n"scale":"1x"\n},
{\n"size":"76x76",\n"idiom":"ipad",\n"filename":"appicon_152.png",\n"scale":"2x"\n},
{\n"size":"83.5x83.5",\n"idiom":"ipad",\n"filename":"appicon_167.png",\n"scale":"2x"\n},
{\n"size":"120x120",\n"idiom":"car",\n"filename":"appicon_120.png",\n"scale":"1x"\n},
{\n"size":"16x16",\n"idiom":"mac",\n"filename":"appicon_16.png",\n"scale":"1x"\n},
{\n"size":"16x16",\n"idiom":"mac",\n"filename":"appicon_32.png",\n"scale":"2x"\n},
{\n"size":"32x32",\n"idiom":"mac",\n"filename":"appicon_32.png",\n"scale":"1x"\n},
{\n"size":"32x32",\n"idiom":"mac",\n"filename":"appicon_64.png",\n"scale":"2x"\n},
{\n"size":"128x128",\n"idiom":"mac",\n"filename":"appicon_128.png",\n"scale":"1x"\n},
{\n"size":"128x128",\n"idiom":"mac",\n"filename":"appicon_256.png",\n"scale":"2x"\n},
{\n"size":"256x256",\n"idiom":"mac",\n"filename":"appicon_256.png",\n"scale":"1x"\n},
{\n"size":"256x256",\n"idiom":"mac",\n"filename":"appicon_512.png",\n"scale":"2x"\n},
{\n"size":"512x512",\n"idiom":"mac",\n"filename":"appicon_512.png",\n"scale":"1x"\n},
{\n"size":"512x512",\n"idiom":"mac",\n"filename":"appicon_1024.png",\n"scale":"2x"\n}\n],
"info":{\n"version":1,\n"author":"xcode"\n}\n}' > "./$2/Images.xcassets/AppIcon.appiconset/Contents.json"

    echo "Complete!"
fi

Kevin, strangely the link does not work when clicked from comment display in Safari. However, if you copy and paste into URL box as text, it works.

Gee you're right, thanks! Here is Andrew's link for people who are coming from the future:
Link to Andrew's Gist