#! /usr/bin/env perl

use strict;
use warnings;

use File::Slurp; # apt install -y libfile-slurp-perl

# It is difficult to tell who is on line with a UI based Linux system
# as all the cli functions assume the other are logged in via cli.
#
# This script determines all "real users" (UUID > 1000, but not 'nobody')
# and then does a ps aux to see if any of them are online.


# Copyright 2024 Daily Data, Inc.
# 
# Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following 
# conditions are met:
#
#   Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
#   Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer 
#   in the documentation and/or other materials provided with the distribution.
#   Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived
#   from this software without specific prior written permission.
# 
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT
# NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
# THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
# OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

# define the version number
# see https://metacpan.org/pod/release/JPEACOCK/version-0.97/lib/version.pod
use version;
our $VERSION = version->declare("0.0.1");

my @users;

my @passwords = read_file( '/etc/passwd' );
while ( my $line = pop @passwords ) {
   next if $line =~ m/^#/;
   my @columns = split( ':', $line );
   push @users, $columns[0] if $columns[2] >= 1000 && $columns[2] < 65534;
}

#print join( "\n", @users );

my $users = join( '\|', @users );
print qx/ps aux | cut -d' ' -f1 | sort | uniq | grep '$users'/;

1;