Article 5783 of comp.lang.perl:
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From: lance@moxley.aiss.uiuc.edu (C Lance Moxley)
Newsgroups: comp.unix.admin,comp.lang.perl,comp.unix.aix
Subject: Summary: Report of Concurrent Users
Followup-To: comp.unix.admin
Date: 11 Sep 1993 03:29:14 GMT
Organization: AISS/Telecom -- University of Illinois at Urbana-Champaign
Lines: 51
Distribution: world
Message-ID: <26rgma$6u4@vixen.cso.uiuc.edu>
NNTP-Posting-Host: moxley.aiss.uiuc.edu

Thanks to all who helped with my quest for a program to
report the concurrent use of an AIX workstation. To those
who wanted a copy of my solution, below is pretty much
exactly what I was looking for.

Thanks again!

#!/usr/local/bin/perl
#
$utmp_format = "A8 A14 A12 s i s s l A16";
$utmp_length = 8+14+12+2+4+2+2+4+16;
$wtmp_file = "/var/adm/wtmp";

%inuse = (); # List of terminals in use
$inuse = 0; # Count of terminals in use

open (WTMP, "<$wtmp_file") || die "Could not open wtmp file $wtmp_file: $!\n";
while ($nread = read(WTMP, $record, $utmp_length)) {
    die "Error reading wtmp file: only $nread bytes returned, $utmp_length expected\n" unless ($nread == $utmp_length);
    #
    ($user, $id, $line, $type, $pid, $termination, $exit, $time, $host) = unpack($utmp_format, $record);
    if ($user ne '') {
        if ($inuse{$line}) {
            warn "Line $line already in use by $inuse{$line}\n";
            $inuse{$line} = $user;
        } else {
            $inuse{$line} = $user;
            $inuse++;
            &timeprint ($time, $inuse);
        }
    } else {
        if ($inuse{$line}) {
            $inuse--;
            delete $inuse{$line};
            &timeprint ($time, $inuse);
        } else {
            warn "Line $line was not known to be in use\n";
        }
    }
}

sub timeprint {
    local ($time, $count) = @_;
    local (@time) = localtime ($time);
    printf "%.2d/%.2d/%.2d-%.2d:%.2d   %d\n",
        $time[4]+1, $time[3], $time[5], $time[2], $time[1], $count;
}
-- 
C Lance Moxley                      Internet: clm@uiuc.edu
AISS/Telecommunications               BITNET: UNETCLM at UICVMC
University of Illinois                  UUCP: uunet!uiucuxc!uiuc.edu!clm