How to display uptime with sleep-mode time excluded

Supporting GNU or Solaris 11 sleep arguments (one or more <double>[smhd] durations, so would also work with traditional implementations that support only one decimal integer number (like on FreeBSD), but not with those accepting more complex arguments like ISO-8601 durations). Using etime instead of etimes as that's more portable (standard Unix).

remaining_sleep_time() { # arg: pid
  ps -o etime= -o args= -p "$1" | perl -MPOSIX -lane '
    %map = qw(d 86400 h 3600 m 60 s 1);
    $F[0] =~ /(\d+-)?(\d+:)?(\d+):(\d+)/;
    $t = -($4+60*($3+60*($2+24*$1)));
    for (@F[2..$#F]) {
      s/\?//g;
      ($n, $p) = strtod($_);
      $n *= $map{substr($_, -$p)} if $p;
      $t += $n
    }
    print $t'
}

(the s/\?//g is to get rid of the ? characters that procps' ps uses as replacement for control characters. Without it, it would fail to parse sleep $'\r1d' or sleep $'\t1d'... Unfortunately, in some locales, including the C locale, it uses . instead of ?. Not much we can do in that case as there's no way to tell a \t5d from a .5d (half day)).

Pass the pid as argument.

That also assumes the argv[0] passed to sleep doesn't contain blanks and that the number of arguments is small enough that it's not truncated by ps.

Examples:

$ sleep infinity & remaining_sleep_time "$!"
Inf
$ sleep 0xffp-6d &
$ remaining_sleep_time "$!"
344249
$ sleep 1m 1m 1m 1m 1m & remaining_sleep_time "$!"
300

For a [[[ddd-]HH:]MM:]SS output instead of just the number of seconds, replace the print $t with:

$output = "";
for ([60,"%02d\n"],[60,"%02d:"],[24,"%02d:"],[inf,"%d-"]) {
  last unless $t;
  $output = sprintf($_->[1], $t % $_->[0]) . $output;
  $t = int($t / $_->[0])
}
printf "%s", $output;

You're comparing apples and oranges.

ps will list the processes running. You're then getting the count of unique process-owning user ids.

uptime will report the users logged on. By using utmp. More details at https://github.com/coreutils/coreutils/blob/master/src/uptime.c#L177

So, comparison of output, highlighting this, below.

# uptime
 16:52:37 up 30 days, 23:32,  1 user,  load average: 0.04, 0.04, 0.05
# w
 16:57:33 up 30 days, 23:37,  1 user,  load average: 0.00, 0.01, 0.05
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
steve    pts/0    cpc79909-stkp12- 16:50    5.00s  0.07s  0.28s sshd: steve [priv]
#


# ps -Af | cut -f1 -d' ' | sort | uniq | wc -l
7
# ps -Af | cut -f1 -d' ' | sort | uniq
chrony
dbus
polkitd
postfix
root
steve
UID
#