Special characters in users file

Hi All, Can we use special characters like $, {, [, ( in the users file?? I have defined some vendor specific attribute in users file. When i escape with \ still im not able to start the server. Whether the freeradius does not allow these characters ?? or we can accept those characters by specifying in different way?? Any help in the earliest will be of great help. Awaiting for your reply. :-) Thanks Sumi