Shell Programming and Scripting

cat test1    --- start time
03/27/15 17:41:00
03/24/15 11:58:04
03/23/15 06:00:00

cat test2    --- end time
03/27/15 17:51:30
03/24/15 18:14:01
03/24/15 07:00:00

Calculating difference using the below command
let DIFF=(`date +%s -d "$b"` - `date +%s -d "$a"`)   // calculating the duration in seconds
echo|date -u -d @${DIFF} +"%H"h" %M"m""  // converting into H:M format.

output

00h 10m   -- correct value
06h 15m   --  correct value
01h 00m   -- In correct value . Instead of 25h printing 1h as its not deducting the day from 24 to 23.

mute@tiny:~$ a='03/23/15 06:00:00' b='03/24/15 07:00:00' diff=$(( $(date +%s -d "$b") - $(date +%s -d "$a") ))
mute@tiny:~$ printf '%dh %02dm\n' $((diff=diff/3600)) $((diff/60))
25h 00m

$ printf '%dh %02dm\n' $((diff/3600)) $(((diff%3600)/60))