#!/usr/bin/python
# Run a command as another user.

import sys, os, pwd, grp, signal, optparse

def main():
	parser = optparse.OptionParser(usage="usage: %prog USER COMMAND ...")
	parser.disable_interspersed_args()
	parser.add_option("--home",
	                  help="Home directory to create and pass in $HOME",
	                  metavar="DIR")
	(options, args) = parser.parse_args()
	if len(args) < 2:
		parser.error("too few arguments")

	username = args[0]
	command = args[1:]

	passwd = pwd.getpwnam(username)
	groups = [group.gr_gid for group in grp.getgrall()
	                       if username in group.gr_mem]

	if options.home:
		home = options.home
		try:
			os.makedirs(home)
		except OSError:
			pass
		os.chown(home, passwd.pw_uid, passwd.pw_gid)
		os.chmod(home, 0755)
	else:
		home = passwd.pw_dir

	os.setgid(passwd.pw_gid)
	os.setgroups(groups)
	os.setuid(passwd.pw_uid)

	os.putenv("LOGNAME", username)
	os.putenv("HOME", home)

	# Python ignores SIGPIPE by default, which will confuse many child
	# processes.
	signal.signal(signal.SIGPIPE, signal.SIG_DFL)

	os.execvp(command[0], command)

if __name__ == "__main__":
	main()