how to calculate total elapsed time - bash

Question

how to calculate elapsed time based on
start time=
[user001a#dev51 logs]# grep 'Recovery Manager'
refresh_03Jun2019_0250.log|head -1|awk -F'on ' '{print $NF}';
Jun 3 02:50:02 2019
[user001a#dev51 logs]#
end time=
[user001a#dev51 logs]# ls -l refresh_03Jun2019_0250.log
-rw-r--r--. 1 user001a grp001a 170050 Jun 3 05:06
refresh_03Jun2019_0250.log
[user001a#dev51 logs]#
Note - stat is missing birth time so stat might not be a good option time calculate file create and modify time:
[user001a#dev51 logs]# stat refresh_03Jun2019_0250.log
File: `refresh_03Jun2019_0250.log'
Size: 170050 Blocks: 344 IO Block: 4096 regular file
Device: 811h/2065d Inode: 1474545 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 219/ user001a) Gid: ( 219/grp001a)
Access: 2019-06-03 05:06:40.830829026 -0400
Modify: 2019-06-03 05:06:40.827828883 -0400
Change: 2019-06-03 05:06:40.827828883 -0400
[user001a#dev51 logs]#
Sample1 output:
StartTime=June 3, 2019 at 2:50:02 am
EndTime=June 3, 2019 at 5:06:40 am
ElapsedTime=2 hours, 16 minutes and 38 seconds
Sample2 output:
ElapsedTime=2 hours, 16 minutes and 38 seconds

Answer 1

Limitation of this solution: Max 23 hours. For more, days need to be added.
StartTime="June 3, 2019 at 2:50:02 am"
EndTime="June 3, 2019 at 5:06:40 am"
StartTimeInEpoch=`echo $StartTime | sed 's/at //g' | date -f- +"%s"`
EndTimeInEpoch=`echo $EndTime | sed 's/at //g' | date -f- +"%s"`
echo $EndTimeInEpoch-$StartTimeInEpoch | bc | sed 's/^/#/g' | date -u -f- "+%_H hours %_M minutes %_S seconds"
Output:
2 hours 16 minutes 38 seconds
Assuming you've got your dates in variables StartTime and EndTime. It's necessary to remove at from them, sed do this. Then both dates are converted to epoch time +"%s" do the trick. -f- tells date to take date from stdin (pipe). Then we can subtract the dates, add # to the beginning and format with date. -u mean UTC time - no time shift.