| The passwddata structure is used to hold information about
entries in the system user data base.  It has at least the following members:
char *pw_nameThe user's login name.
char *pw_passwd.The encrypted password string.
uid_t pw_uidThe user ID number.
gid_t pw_gidThe user's default group ID number.
char *pw_gecosA string typically containing the user's real name, and possibly other
information such as a phone number.
char *pw_dirThe user's home directory, or initial working directory.  This might be
a null pointer, in which case the interpretation is system-dependent.
char *pw_shellThe user's default shell, or the initial program run when the user logs in. 
This might be a null pointer, indicating that the system default should
be used. 
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