How can I sort a files contents beyond two fields (columns)? I want to first sort by month, then by day of the month, then by time of the day.

I am also curious to know if the expr command supports floating point numbers?

The sort command can handle up to nine fields so you should have no preoblem. If you ever need more than nine you can often disign the record to sorted to have sort keys next to one another and then treat them as a single combined field.

No expr cannot handle floating point. But bc can handle fixed point and this can be used to do non-integer arithmetic:

A=1.2
B=.5
C=`echo $A + $B | bc`
echo $C