A quick script to automatically change the Xamarin Studio Apple SDK from Xcode4 (for iOS 5.1 development) to Xcode5 (for iOS 7.0 development). The script will also automatically update the first (and only) csproj in the current directory and finally launch Xamarin Studio with the desired configuration.

xamarin_switch.py

#!/usr/bin/python
import sys, os, re
import getpass, getopt
import xml.etree.ElementTree as ET

pref_xcode4_loc = "/Applications/Xcode.app"
pref_xcode5_loc = "/Applications/Xcode5-DP.app"
pref_loc = "/Users/%s/Library/Preferences/XamarinStudio-4.0/MonoDevelopProperties.xml" % (getpass.getuser())
pref_key = "MonoDevelop.MacDev.AppleSdkRoot"

csproj_xcode4_val = "6.1"
csproj_xcode5_val = "7.0"
csproj_sdk_ele = "MtouchSdkVersion"

def update_prefs(version_xcode):
  tree = ET.parse(pref_loc)
	root = tree.getroot()
	prop = root.findall("Property[@key='%s']" % (pref_key))[0]
	prop.attrib["value"] = version_xcode
	tree.write(pref_loc)

def update_csproj(csproj_path, csproj_val):
	# determine the old value of the SDK based on what the new one is
	old_xcode = csproj_xcode4_val
	if(csproj_val == csproj_xcode4_val):
		old_xcode = csproj_xcode5_val
	# just do some old school regex to avoid MS XML namespaces
	with open(csproj_path) as f:
		tmp_csproj_path = csproj_path + ".tmp"
		out = open(tmp_csproj_path, "w")
		pattern = "\<{0}\>{1}\<\/{0}\>".format(csproj_sdk_ele, old_xcode)
		replace = "<{0}>{1}</{0}>".format(csproj_sdk_ele, csproj_val)
		for line in f:
			out.write(re.sub(pattern, replace, line))
		out.close()
		os.rename(tmp_csproj_path, csproj_path)

def find_files_with_ext(extension):
	return [f for f in os.listdir('.') if os.path.isfile(f) and os.path.splitext(f)[1] == extension]
		
def usage():
	print "usage: xamarian_switch.py <xcode-version>\nBe sure to only have 1 csproj file in the current directory\n"
	sys.exit(2)

if __name__ == "__main__":
	
	if len(sys.argv) != 2:
		usage()

	version_xcode = ""
	csproj_val = ""

	if sys.argv[1].lower() in [ "4", "xcode4" ]:
		version_xcode = pref_xcode4_loc
		csproj_val = csproj_xcode4_val

	if sys.argv[1].lower() in [ "5", "xcode5" ]:
		version_xcode = pref_xcode5_loc 
		csproj_val = csproj_xcode5_val

	if version_xcode == "" or csproj_val == "":
		usage()

	update_prefs(version_xcode)
	print "Updated AppleSdkRoot to %s" % (version_xcode)

	csproj_paths = find_files_with_ext(".csproj")
	if csproj_paths == None or len(csproj_paths) == 0:
		usage()

	if len(csproj_paths) != 1:
		usage()

	update_csproj(csproj_paths[0], csproj_val)
	print "Updated %s's MtouchSdkVersion to SDK Version of %s" % (csproj_paths[0], csproj_val)

	sln = find_files_with_ext(".sln")[0]
	print "Opening %s with Xamarin Studio using %s" % (sln, version_xcode)
	os.system("open -n /Applications/Xamarin\ Studio.app ./" + sln)