What's the easiest way to get a user's full name on a Linux/POSIX system?

Question

I could grep through /etc/passwd but that seems onerous. 'finger' isn't installed and I'd like to avoid that dependency. This is for a program so it would be nice if there was some command that let you just access user info.

Answer 1

On a modern glibc system, use this command:

getent passwd "username" | cut -d ':' -f 5

That'll get you the passwd entry of the specified user, independent of the underlying NSS module.

Read the manpage of getent.

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If you're already programming, you can use the getpwnam() C-Function:

struct passwd *getpwnam(const char *name);

The passwd struct has a pw_gecos member which should contain the full name of the user.

Read the manpage of getpwnam().

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Be aware that many systems use this field for more than the full name of the user. The most common convention is to use a comma (,) as separator within the field and place the users real name first.

Answer 2

Are you looking for getpwnam?

Answer 3

You don't specify a programming language, so I'll assume you want to use the shell; here's an answer for the bash shell.

Two steps to this: get the appropriate record, then get the field you want from that record.

First, getting the account record is done by querying the passwd table:

$ user_name=foo
$ getent passwd $user_name
foo:x:1023:1025:Fred Nurk,,,:/home/foo:/bin/bash

For hysterical raisins, the full name of the user is recorded in a field called the “GECOS” field; to complicate matters, this field often has its own structure with the full name as just one of several optional sub-fields. So anything that wants to get the full name from the account record needs to parse both these levels.

$ user_record=$(getent passwd $user_name)
$ user_gecos_field=$(echo "$user_record" | cut -d ':' -f 5)
$ user_full_name=$(echo "$user_gecos_field" | cut -d ',' -f 1)
$ echo $user_full_name
Fred Nurk

Your programming language probably has a library function to do this in fewer steps. In C, you'd use the ‘getpwnam’ function and then parse the GECOS field.

Answer 4

Just in case you want to do this from C, try something like this:

#include <sys/types.h>
#include <pwd.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>

/* Get full name of a user, given their username. Return 0 for not found,
   -1 for error, or 1 for success. Copy name to `fullname`, but only up
   to max-1 chars (max includes trailing '\0'). Note that if the GECOS
   field contains commas, only up to to (but not including) the first comma
   is copied, since the commas are a convention to add more than just the
   name into the field, e.g., room number, phone number, etc. */
static int getfullname(const char *username, char *fullname, size_t max)
{
    struct passwd *p;
    size_t n;

    errno = 0;
    p = getpwnam(username);
    if (p == NULL && errno == 0)
        return 0;
    if (p == NULL)
        return -1;
    if (max == 0)
        return 1;
    n = strcspn(p->pw_gecos, ",");
    if (n > max - 1)
        n = max - 1;
    memcpy(fullname, p->pw_gecos, n);
    fullname[n] = '\0';
    return 1;
}

int main(int argc, char **argv)
{
    int i;
    int ret;
    char fullname[1024];

    for (i = 1; i < argc; ++i) {
        ret = getfullname(argv[i], fullname, sizeof fullname);
        if (ret == -1)
            printf("ERROR: %s: %s\n", argv[i], strerror(errno));
        else if (ret == 0)
            printf("UNKONWN: %s\n", argv[i]);
        else
            printf("%s: %s\n", argv[i], fullname);
    }
    return 0;
}