Looking for command to help with program
 

I need to be able to calculate the amount of time a user has been logged onto the system for.

UsrMin=$(who | grep $1 | cut -c30-35)
Time=$(date +%H:%M)
echo $UsrMin
echo $Time
echo LoginTime CurrentTime
echo ' '$UsrMin - $Time
~

conntime f132a13
20:57
21:18
LoginTime CurrentTime
20:57 - 21:18


This is as close as I could get to figuring out my problem. It wouldn't allow me to do the subtraction so I left it like this. Please help!

Extending that method, you'd convert the hrs to mins, add the extra mins, then subtract 'now' from 'then', optionally converting the result to hrs and mins if diff_result > 60.
Of course, this only works when the login time is in the same day as the current time. For a more general approach, you'd have to calc the date diff as well, probably using the various date format options.

Personally, if this was for a serious eg prod system, I'd likely do it in Perl as it has plenty of date calc routines.