# setaliasent

## NAME



           setaliasent, endaliasent, getaliasent, getaliasent_r,
           getaliasbyname, getaliasbyname_r - read an alias entry
    


## LIBRARY



           Standard C library (_libc_ , _-lc_)
    


## SYNOPSIS



           **#include <aliases.h>**
    
           **void setaliasent(void);**
           **void endaliasent(void);**
    
           **struct aliasent *getaliasent(void);**
           **int getaliasent_r(** size_t size;
                                **struct aliasent *restrict** _result_**,**
                                **char** _buffer_**[restrict** _size_**], size_t** _size_**,**
                                **struct aliasent **restrict** _res_**);**
    
           **struct aliasent *getaliasbyname(const char ***_name_**);**
           **int getaliasbyname_r(** size_t size;
                                **const char *restrict** _name_**,**
                                **struct aliasent *restrict** _result_**,**
                                **char** _buffer_**[restrict** _size_**], size_t** _size_**,**
                                **struct aliasent **restrict** _res_**);**
    


## DESCRIPTION



           One of the databases available with the Name Service Switch (NSS)
           is the aliases database, that contains mail aliases.  (To find out
           which databases are supported, try _getent --help_.)  Six functions
           are provided to access the aliases database.
    
           The **getaliasent**() function returns a pointer to a structure
           containing the group information from the aliases database.  The
           first time it is called it returns the first entry; thereafter, it
           returns successive entries.
    
           The **setaliasent**() function rewinds the file pointer to the
           beginning of the aliases database.
    
           The **endaliasent**() function closes the aliases database.
    
           **getaliasent_r**() is the reentrant version of the previous function.
           The requested structure is stored via the first argument but the
           programmer needs to fill the other arguments also.  Not providing
           enough space causes the function to fail.
    
           The function **getaliasbyname**() takes the name argument and searches
           the aliases database.  The entry is returned as a pointer to a
           _struct aliasent_.
    
           **getaliasbyname_r**() is the reentrant version of the previous
           function.  The requested structure is stored via the second
           argument but the programmer needs to fill the other arguments
           also.  Not providing enough space causes the function to fail.
    
           The _struct aliasent_ is defined in _< aliases.h>_:
    
               struct aliasent {
                   char    *alias_name;             /* alias name */
                   size_t   alias_members_len;
                   char   **alias_members;          /* alias name list */
                   int      alias_local;
               };
    


## RETURN VALUE



           The functions **getaliasent_r**() and **getaliasbyname_r**() return a
           nonzero value on error.
    


## FILES



           The default alias database is the file _/etc/aliases_.  This can be
           changed in the _/etc/nsswitch.conf_ file.
    


## ATTRIBUTES



           For an explanation of the terms used in this section, see
           attributes(7).
           ┌───────────────────────────────┬───────────────┬────────────────┐
           │ **Interface** │ **Attribute** │ **Value** │
           ├───────────────────────────────┼───────────────┼────────────────┤
           │ **setaliasent**(), **endaliasent**(), │ Thread safety │ MT-Safe locale │
           │ **getaliasent_r**(),              │               │                │
           │ **getaliasbyname_r**()            │               │                │
           ├───────────────────────────────┼───────────────┼────────────────┤
           │ **getaliasent**(),                │ Thread safety │ MT-Unsafe      │
           │ **getaliasbyname**()              │               │                │
           └───────────────────────────────┴───────────────┴────────────────┘
    


## STANDARDS



           GNU.
    


## EXAMPLES



           The following example compiles with _gcc example.c -o example_.  It
           will dump all names in the alias database.
    
           #include <aliases.h>
           #include <errno.h>
           #include <stdio.h>
           #include <stdlib.h>
    
           int
           main(void)
           {
               struct aliasent *al;
    
               setaliasent();
               for (;;) {
                   al = getaliasent();
                   if (al == NULL)
                       break;
                   printf("Name: %s\n", al->alias_name);
               }
               if (errno) {
                   perror("reading alias");
                   exit(EXIT_FAILURE);
               }
               endaliasent();
               exit(EXIT_SUCCESS);
           }
    


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