def execute_su_command(db, args):
source = fishbase.get_credentials_file(username=args[0])
dest = fishbase.get_credentials_file()
shutil.copyfile(source, dest)
db = Fluidinfo(Credentials(filename=dest))
username = db.credentials.username
file = args[0].decode(DEFAULT_ENCODING)
extra = u'' if args[0] == username else (u' (file %s)' % file)
db.Print(u'Credentials set to user %s%s.' % (username, extra))