setaliasent(3)

✨ setaliasent(3) ✨

okay bestie, so this is a page from the Library Functions Manual — we're talking setaliasent(3) and the whole lil friend group of functions that read alias entries. mail aliases, to be specific. let's get into it 💖

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🌸 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, and it contains mail aliases. (To find out which databases are supported, try getent --help.) And you get six functions to access the aliases database. six!! a whole squad 🫶

• 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 💜

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).

• setaliasent(), endaliasent(), getaliasent_r(), getaliasbyname_r() — Thread safety: MT-Safe locale
• getaliasent(), getaliasbyname() — Thread safety: MT-Unsafe

no cap, that MT-Unsafe on the two plain getters is real — the *_r versions are the ones you want when threads are in the room 💀

⭐ STANDARDS ⭐

GNU.

🦋 HISTORY 🦋

The NeXT system has similar routines:

#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. slay.

#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)

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and that's the whole page bestie 🎀 this one's from Linux man-pages 6.20, dated 2026-02-08 — go forth and rewind those alias file pointers, and remember: check errno, use the _r versions, and always endaliasent() when you're done. mwah 💜✨