Linux - users online and logged in after a specified date

Question

I have to write a shell script that returns all users online who logged in after a specified date.

I tried

who | cut -d' ' -f1 | sort | uniq

but I don't know how to put in the condition for the date to be later than the date I give manually.

Answer 1

You can tackle this issue in a number of ways, I usually prefer using epoch to compare dates.

The date command can easily convert to epoch (seconds since 1970-01-01 00:00:00 UTC):

Current date/time in epoch:

date +%s
1479994078

Convert any date to epoch:

date --date="19-FEB-12" +%s
1329620400

You can easily compare the dates in bash expanding the commands:

if [[ $(date +%s) >= $(date --date="19-FEB-12" +%s) ]]
  then
    ...
fi