setaliasent(3) Library Functions Manual setaliasent(3)
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(struct aliasent *restrict result,
char buffer[restrict .buflen], size_t buflen,
struct aliasent **restrict res);
struct aliasent *getaliasbyname(const char *name);
int getaliasbyname_r(const char *restrict name,
struct aliasent *restrict result,
char buffer[restrict .buflen], size_t buflen,
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 pro-
vided 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 pro-
grammer 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 at-
tributes(7).
┌─────────────────────────────────────┬───────────────┬────────────────┐
│Interface │ Attribute │ Value │
├─────────────────────────────────────┼───────────────┼────────────────┤
│setaliasent(), endaliasent(), │ Thread safety │ MT-Safe locale │
│getaliasent_r(), getaliasbyname_r() │ │ │
├─────────────────────────────────────┼───────────────┼────────────────┤
│getaliasent(), getaliasbyname() │ Thread safety │ MT-Unsafe │
└─────────────────────────────────────┴───────────────┴────────────────┘
STANDARDS
These routines are glibc-specific. The NeXT system has similar rou-
tines:
#include <aliasdb.h>
void alias_setent(void);
void alias_endent(void);
alias_ent *alias_getent(void);
alias_ent *alias_getbyname(char *name);
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);
}
SEE ALSO
getgrent(3), getpwent(3), getspent(3), aliases(5)
Linux man-pages 6.03 2022-12-15 setaliasent(3)
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