Hello,
I am trying to set up an el-cheapo attendance system that only calculates how late the person has come with reference to a fixed office time. I don't want to use any database+server thing as that is complex and users are less than 20. I am thinking of a simple approach with cheap and simple biometrics to prevent impersonation. A cheap web cam will click light thumbnails and a timestamp will be generated. Every month a file will be generated after which the photos can be erased automatically. The result file will be a .csv one that can be imported in any Office application.
I am stuck at the point of calculating time difference. There doesn't seem to be a direct command that will calculate time difference in HH:MM format. This link mentions a work around http://www.cyberciti.biz/faq/shell-script-to-get-the-time-difference/ but it first converts time into %s which is the number of seconds since 1970. However every day for the fixed opening time, say 10:00 this figure is not constant. One way out is that every day the %s figure is generated at exactly 10:00 and this is then 'diff'ed with the user's attendance time in %s. This is then divided by 60.
Is there a simpler bash command that I may have overlooked that simply takes in 10:17 and 10:00 and says 00:17?