/usr/share/munin/plugins/apc_nis is in munin-plugins-extra 2.0.19-3ubuntu0.3.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122  | #!/usr/bin/perl -w
# -*- perl -*-
=head1 NAME
apc_nis - Plugin to monitor APC UPS via the nis port of apcupsd
=head1 CONFIGURATION
The following configuration parameters are used by this plugin
 [apc_nis]
  env.host     - hostname to connect to
  env.port     - port number to connect to
=head2 DEFAULT CONFIGURATION
 [apc_nis]
  env.host 127.0.0.1
  env.port 3551
=head1 MAGIC MARKERS
 #%# family=contrib
 #%# capabilities=autoconf
=cut
use IO::Socket;
use strict;
if($ARGV[0] and $ARGV[0] eq "autoconf") {
    print "yes\n";
    exit 0;
}
my $host = exists $ENV{'host'} ? $ENV{'host'} : "127.0.0.1";
my $port = exists $ENV{'port'} ? $ENV{'port'} : "3551";
my $sock = new IO::Socket::INET (
    PeerAddr => $host,
    PeerPort => $port,
    Proto => 'tcp'
    );
die "Could not create socket: $!\n" unless $sock;
my $buf = pack("CC", 0, 6);
print $sock $buf;
print $sock "status\n";
if($ARGV[0] and $ARGV[0] eq "config") {
    # Test for some capabilities.
    my $has_temperature = 0, my $line_volt_min, my $line_volt_max;
    my $line;
    do {
        $line = <$sock>;
        chomp($line);
        if ($line =~ /\WITEMP /) {
            $has_temperature = 1;
        } elsif ($line =~ /\WLOTRANS /) {
	    $line =~ s/.* (\d+.\d+).*/$1/;
	    $line_volt_min = $line;
        } elsif ($line =~ /\WHITRANS /) {
	    $line =~ s/.* (\d+.\d+).*/$1/;
	    $line_volt_max = $line;
	}
    } while(!($line =~ /END APC/));
    close($sock);
    print "graph_title APC UPS measurements\n";
    print "graph_args -l 0 --base 1000\n";
    print "graph_vlabel A bit of all (Volt, time, %)\n";
    print "graph_info Values received for apcupsd available at $host:$port\n";
    print "battery_volt.label batt volt (V)\n";
    print "battery_volt.type GAUGE\n";
    print "battery_volt.max 300\n";
    print "battery_charge.label batt charge (%)\n";
    print "battery_charge.type GAUGE\n";
    print "battery_charge.max 100\n";
    print "line_volt.label line (V)\n";
    print "line_volt.type GAUGE\n";
    print "line_volt.max 300\n";
    print "line_volt.warning ${line_volt_min}:${line_volt_max}\n";
    print "load.label ups load (%)\n";
    print "load.type GAUGE\n";
    print "time_left.label time left (min)\n";
    print "time_left.type GAUGE\n";
    if ($has_temperature) {
        print "temperature.label internal temperature (°C)\n";
        print "temperature.type GAUGE\n";
    }
    exit 0;
}
my $line;
do {
    $line = <$sock>;
    chomp($line);
    if($line =~ /\WBATTV /) {
        $line =~ s/.* (\d+.\d+).*/$1/;
        print "battery_volt.value $line\n";
    } elsif($line =~ /\WLINEV /) {
        $line =~ s/.* (\d+.\d+).*/$1/;
        print "line_volt.value $line\n";
    } elsif($line =~ /\WLOADPCT /) {
        $line =~ s/.* (\d+.\d+).*/$1/;
        print "load.value $line\n";
    } elsif($line =~ /\WBCHARGE /) {
        $line =~ s/.* (\d+.\d+).*/$1/;
        print "battery_charge.value $line\n";
    } elsif($line =~ /\WTIMELEFT /) {
        $line =~ s/.* (\d+.\d+).*/$1/;
        print "time_left.value $line\n";
    } elsif($line =~ /\WITEMP /) {
        $line =~ s/.* (\d+.\d+).*/$1/;
        print "temperature.value $line\n";
    }
} while(!($line =~ /END APC/));
close($sock);
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