Answer Posted / alf55

There is one thing different between who and this command in
that there are processes on the system that are run as
daemons and they will end up in the count (so nicely
described in answer #3). But as pointed out in answer #2,
it does include the header line entry in its count. To fix
that problem, (date ; ps -ef | sed '1 d' | cut -d\ -f1 |
sort -u | wc -l) >> Activity.log
could be used.

The "sed '1 d' " will delete the first line (removing the
header line

the "cut -d\ -f1" (Note there a space after the "\" and
then another space for the field separator.) which is the
same as "awk '{print $1}'".

the "sort -u" does the same work as "sort | uniq".

The ">> Activity.log" is a redirection that appends so date
and the count is append to the current data in the file
"Activity.log". Note: is will not show the ">>" as shown in
answer #3.

Examples of users that will show up in this script that will
not show up using "who | cut -d\ -f1 | sort -u | wc -l":

apache
messagebus
haldaemon
dhcp
lighttp
postmaster
ldap
mysql
postgres
memcached
openvpn

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