modify a user account
-a - Add the user to the supplementary group(s). Use only with the -G option.
-c - The new value of the user's password file comment field.
-d - The user's new login directory.
-e - The date on which the user account will be disabled.
-f - The number of days after a password expires until the account is permanently disabled.
-g - The group name or number of the user's new initial login group. The group must exist.
-G - A list of supplementary groups which the user is also a member of.
-l <new_login> - The name of the user will be changed from LOGIN to NEW_LOGIN.
-m - Move the content of the user's home directory to the new location. This option is only valid in combination with the -d option.
-p - The encrypted password, as returned by crypt.
-s - The name of the user's login shell.
-u - The new numerical value of the user's ID.