'\" t
.\" Copyright 2003 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
.\"
.\" SPDX-License-Identifier: GPL-1.0-or-later
.\"
.\" Polished a bit, added a little, aeb
.\"
.TH setaliasent 3 2023-10-31 "Linux man-pages 6.7"
.SH NAME
setaliasent, endaliasent, getaliasent, getaliasent_r,
getaliasbyname, getaliasbyname_r \- read an alias entry
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <aliases.h>
.P
.B "void setaliasent(void);"
.B "void endaliasent(void);"
.P
.B "struct aliasent *getaliasent(void);"
.BI "int getaliasent_r(struct aliasent *restrict " result ,
.BI "                     char " buffer "[restrict ." buflen "], \
size_t " buflen ,
.BI "                     struct aliasent **restrict " res );
.P
.BI "struct aliasent *getaliasbyname(const char *" name );
.BI "int getaliasbyname_r(const char *restrict " name ,
.BI "                     struct aliasent *restrict " result ,
.BI "                     char " buffer "[restrict ." buflen "], \
size_t " buflen ,
.BI "                     struct aliasent **restrict " res );
.fi
.SH 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
.IR "getent \-\-help" .)
Six functions are provided to access the aliases database.
.P
The
.BR 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.
.P
The
.BR setaliasent ()
function rewinds the file pointer to the beginning of the
aliases database.
.P
The
.BR endaliasent ()
function closes the aliases database.
.P
.BR 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.
.P
The function
.BR getaliasbyname ()
takes the name argument and searches the aliases database.
The entry is returned as a pointer to a
.IR "struct aliasent" .
.P
.BR 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.
.P
The
.I "struct aliasent"
is defined in
.IR <aliases.h> :
.P
.in +4n
.EX
struct aliasent {
    char    *alias_name;             /* alias name */
    size_t   alias_members_len;
    char   **alias_members;          /* alias name list */
    int      alias_local;
};
.EE
.in
.SH RETURN VALUE
The functions
.BR getaliasent_r ()
and
.BR getaliasbyname_r ()
return a nonzero value on error.
.SH FILES
The default alias database is the file
.IR /etc/aliases .
This can be changed in the
.I /etc/nsswitch.conf
file.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR setaliasent (),
.BR endaliasent (),
.BR getaliasent_r (),
.BR getaliasbyname_r ()
T}	Thread safety	MT-Safe locale
T{
.na
.nh
.BR getaliasent (),
.BR getaliasbyname ()
T}	Thread safety	MT-Unsafe
.TE
.SH STANDARDS
GNU.
.SH HISTORY
The NeXT system has similar routines:
.P
.in +4n
.EX
#include <aliasdb.h>
\&
void alias_setent(void);
void alias_endent(void);
alias_ent *alias_getent(void);
alias_ent *alias_getbyname(char *name);
.EE
.in
.SH EXAMPLES
The following example compiles with
.IR "gcc example.c \-o example" .
It will dump all names in the alias database.
.P
.\" SRC BEGIN (setaliasent.c)
.EX
#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\en", al\->alias_name);
    }
    if (errno) {
        perror("reading alias");
        exit(EXIT_FAILURE);
    }
    endaliasent();
    exit(EXIT_SUCCESS);
}
.EE
.\" SRC END
.SH SEE ALSO
.BR getgrent (3),
.BR getpwent (3),
.BR getspent (3),
.BR aliases (5)
.\"
.\" /etc/sendmail/aliases
.\" Yellow Pages
.\" newaliases, postalias