IPhone – How to download pkg files from iTunes

You can use the iPhone Configuration Utility to side-load apps onto an iOS device without 'syncing' and erasing your current content.

Config Utility for Mac
Config Utility for Windows

Keep in mind, though, that this will only work if the app is correctly codesigned and the device is correctly provisioned.

It's easy enough to create a shell script which checks for a few conditions and then takes the appropriate action.

I've put mine at http://dl.dropbox.com/u/18414/bin/unpkg.sh but will copy the initial version below:

#!/bin/zsh
#
#   Author:     Timothy J. Luoma
#   Email:      luomat at gmail dot com
#   Date:       2011-12-29
#
#   Purpose:    extract .pkg files, either xar archives or directory
#               
#   URL:       http://dl.dropbox.com/u/18414/bin/unpkg.sh
#   
#   See also:  http://apple.stackexchange.com/questions/34957/foolproof-way-of-extracting-pkg-files

NAME="$0:t"

    # Brief explanation of how program works
USAGE="$NAME is meant to extract package files. (Filenames must end in .pkg). Can handle both .pkg directories or xar archives.

Usage: $NAME /path/to/foo.pkg
"

    # in case of emergency, report error and exit
die ()
{
    echo "$NAME: $@"
    exit 1
}

    # if not given any input, explain how to use it
if [ "$#" = "0" ]
then
        die "$USAGE"    
fi

    # put whatever we get as an argument into a variable
INPUT="$@"

    # does the input actual refer to an existing file?
    # if not, exit
[[ -e "$INPUT" ]]       || die "$INPUT does not exist"

    # get the extension of the input. i.e. if we are
    # given "foo.pkg" this will just be "pkg"
EXT="$INPUT:e"

    # check to make sure that the extension is 'pkg'
    # because that's what we're looking for
[[ "$EXT" = "pkg" ]]    || die "$INPUT is not a pkg"

TYPE=`file -b "$INPUT"`

case "$TYPE" in 
    directory)
                gzcat "$INPUT/Contents/Archive.pax.gz" | pax -r

    ;;

    "xar archive - version 1")
                # Put whatever commands you want here
                :
    ;;


    *)
            die "$USAGE"    
    ;;

esac



exit 0
#EOF

zsh has been included in Mac OS X for several releases now. I prefer it over /bin/sh because… well, let's not get into a "my shell is better than your shell" war, because my shell would win :-)

In any event, zsh makes things a little easier and a little nicer, and it's included, so there's no reason not to use it, IMO. Especially for a OS X-specific script like this.

This was tested on 10.7.