gethostbyname function

Get host record given name

gethostbyname NAME

These routines perform the same functions as their counterparts in the system library. In list context, the return values from the various get routines are as follows:

    ($name,$passwd,$uid,$gid,
       $quota,$comment,$gcos,$dir,$shell,$expire) = getpw*
    ($name,$passwd,$gid,$members) = getgr*
    ($name,$aliases,$addrtype,$length,@addrs) = gethost*
    ($name,$aliases,$addrtype,$net) = getnet*
    ($name,$aliases,$proto) = getproto*
    ($name,$aliases,$port,$proto) = getserv*

(If the entry doesn't exist you get a null list.)

In scalar context, you get the name, unless the function was a lookup by name, in which case you get the other thing, whatever it is. (If the entry doesn't exist you get the undefined value.) For example:

    $uid   = getpwnam($name);
    $name  = getpwuid($num);
    $name  = getpwent();
    $gid   = getgrnam($name);
    $name  = getgrgid($num;
    $name  = getgrent();
    #etc.

In getpw*() the fields $quota, $comment, and $expire are special cases in the sense that in many systems they are unsupported. If the $quota is unsupported, it is an empty scalar. If it is supported, it usually encodes the disk quota. If the $comment field is unsupported, it is an empty scalar. If it is supported it usually encodes some administrative comment about the user. In some systems the $quota field may be $change or $age, fields that have to do with password aging. In some systems the $comment field may be $class. The $expire field, if present, encodes the expiration period of the account or the password. For the availability and the exact meaning of these fields in your system, please consult your getpwnam(3) documentation and your pwd.h file. You can also find out from within Perl which meaning your $quota and $comment fields have and whether you have the $expire field by using the Config module and the values d_pwquota, d_pwage, d_pwchange, d_pwcomment, and d_pwexpire.

The $members value returned by getgr*() is a space separated list of the login names of the members of the group.

For the gethost*() functions, if the h_errno variable is supported in C, it will be returned to you via $? if the function call fails. The @addrs value returned by a successful call is a list of the raw addresses returned by the corresponding system library call. In the Internet domain, each address is four bytes long and you can unpack it by saying something like:

    ($a,$b,$c,$d) = unpack('C4',$addr[0]);

If you get tired of remembering which element of the return list contains which return value, by-name interfaces are also provided in modules: File::stat, Net::hostent, Net::netent, Net::protoent, Net::servent, Time::gmtime, Time::localtime, and User::grent. These override the normal built-in, replacing them with versions that return objects with the appropriate names for each field. For example:

   use File::stat;
   use User::pwent;
   $is_his = (stat($filename)->uid == pwent($whoever)->uid);

Even though it looks like they're the same method calls (uid), they aren't, because a File::stat object is different from a User::pwent object.