Fix user's default shell in their user record in /Local/Default

fixUserShell.py

#!/usr/bin/python


'''
Author:  Calum Hunter
Date:    April 16 2018
Version: 1.0

This script will get the current UserShell
value set in the users record in /Local/Default
if this UserShell varies from '/bin/bash'
we will change it to ensure it is set to '/bin/bash'

Note: In order to perform the change of the users shell
dscl must be run with root or sudo.

This script should be run as a login script with outset
or a similar tool - noting that it must be run 'as root' 
'''

import sys
import subprocess
from SystemConfiguration import SCDynamicStoreCopyConsoleUser

# Set to 'True' to enable debug for extra output 
debug = True

# Define the 'Correct' UserShell.
# This is the UserShell we _SHOULD_ be setting
correctUserShell = '/bin/bash'

# Start by getting the details of the currently logged in console user
# use python and the SysConfig moduleto avoid incorrect information 
# being returned from other tools like whoami or other posix tools
loggedInUser = (SCDynamicStoreCopyConsoleUser(None, None, None) or [None])
loggedInUser = [loggedInUser,""][loggedInUser in [u"loginwindow", None, u""]]

# Assign the elements from loggedInUser dict to variables
loggedInUser_shortname = loggedInUser[0]
loggedInUser_uid = loggedInUser[1]
loggedInUser_gid = loggedInUser[2]

# Prep the command to return the UserShell
getShellCmd = [
	'/usr/bin/dscl', '/Local/Default', '-read', 
	'/Users/'+loggedInUser_shortname, 'UserShell'
	]

# Run the command above, split the result to obtain the 2nd element which
# is actually the UserShell, then we strip off the \n new line at the end
currentUserShell = subprocess.check_output(getShellCmd).split(': ')[1].strip()

# Print out some information here, if we have debug set to True
if debug:
	print ('Current Logged in user details:')
	print (' - Shortname: %s') % loggedInUser_shortname
	print (' - UID: %s') % loggedInUser_uid
	print (' - GID: %s') % loggedInUser_gid
	print (' - Current UserShell: %s') % currentUserShell
	print ('')

# If our UserShell is _NOT_ what our correctUserShell is, then we should use
# dscl to change the UserShell to $correctUserShell
if currentUserShell != correctUserShell:
	# prep the change command
	changeShellCmd = [
		'/usr/bin/dscl', '/Local/Default', '-change', 
		'/Users/'+loggedInUser_shortname, 'UserShell', 
		currentUserShell, correctUserShell
		]
	# Notify that the incorrect shell was detected and we
	# are going to change it if debug enabled
	if debug:
		print ('[ERROR] Current UserShell does NOT match what we expect!')
		print ('- Current UserShell: %s') % currentUserShell
		print ('- Correct UserShell: %s') % correctUserShell
		print ('')
		print (' - Attempting to change UserShell to: %s ...') % correctUserShell
	# Try to perform the change of Usershell
	try:
		changeUserShell = subprocess.check_output(changeShellCmd, stderr=subprocess.STDOUT)
		if debug:
			print ('[OK] - UserShell changed successfully!')
	# If we get a non zero return code from dscl, then trap it and raise an exception
	except subprocess.CalledProcessError as changeShellError:
		print ('[ERROR] There was an error trying to change the UserShell with dscl')
		print (' - Ensure you are running this script with root privilegs.')
		print ('')
		print (' - dscl exit code: %s') % changeShellError.returncode
		print (' - dscl error output: %s') % changeShellError.output
else:
	if debug:
		print ('- Current UserShell matches what we expect, no changes required.')
	sys.exit()