How does bash calculate time difference?
Bash variable SECONDS (if SECONDS is unset it loses its special property).
- Setting the value of SECONDS to 0: SECONDS=0 sleep 1 # Process to execute elapsedseconds=$SECONDS.
- Storing the value of the variable SECONDS at the start: a=$SECONDS sleep 1 # Process to execute elapsedseconds=$(( SECONDS – a ))
How does Linux calculate elapsed time?
Measure elapsed time internally in a script
- START_TIME=$(date +%s)
- sleep 1 # put some real task here instead of sleeping.
- END_TIME=$(date +%s)
- echo “It took $(($END_TIME – $START_TIME)) seconds to sleep of 1 second…”
How to subtract time using date and Bash Stack Exchange?
Debugging a bit more, the parsing seems to be: 2019-01-19T05:00:00 – 2 ( -2 being the timezone), and hours (= 1 hour), with an implied addition. It becomes easier to see if you use minutes instead:
How to do subtraction arithmetics with Linux date command?
Every time the command is executed it will create a file with the current date included in the file name. We do not usually want to keep all backup files indefinitely or until they consume all available free space. This is where the subtraction arithmetics with Linux date command becomes handy.
How to subtract two weeks from a date?
In this case here as a simple example on how to the do all above using epoch time. epoch time is simply a number of seconds since “Jan 1, 1970 00:00:00”. Therefore, epoch time “1” using universal time is: Lets see how we can subtract 2 weeks, 3 days, and 23 seconds from a current date using epoch time.
When to use + / to subtract time?
The use of +/- when there is no timezone specified in the timestamp triggers an attempt to match a timezone next, before anything else is parsed. (Though you cannot arbitrarily use “Z”, it works in my zone, but that makes it a UTC/GMT zone timestamp – use your own zone, or %z/%Z by appending $ {TZ:-$ (date +%z)} to the timestamp instead.)