Round current time up and down - bash

Question

I'm trying to figure out how to get the current hour rounded down to start of the hour and the next hour in bash?
For example, if I run my script:
./printHour.sh
and let's say the current time at execution is 13:04:12 - it would print
current hour is: 13:00:00
next hour is: 14:00:00
Progress so far: (but this gives 1hour ago so it does not work) - any ideas?
lastHour=$(date -d '1 hour ago' "+%H:%M:%S")
echo "current hour is: "$lastHour

Answer 1

You can use this utility function:
hrdt() { date -d "${1?} hour ago" '+%H:00:00'; }
Testing:
> hrdt
bash: 1: parameter not set
> hrdt 0
08:00:00
> hrdt 1
07:00:00
> hrdt 2
06:00:00
> hrdt 3
05:00:00

Answer 2

Could you please try following, written and tested as per shown samples, my date is GNU date version.
cat script.bash
#!/bin/bash
currentHour=$(date "+%H:00:00")
nextHour=$(date -d '+1 hour' "+%H:00:00")
echo "current hour is: $currentHour"
echo "next hour is: $nextHour"
When I run above script I get as follows:
current hour is: 06:00:00
next hour is: 07:00:00

Answer 3

Seems like you don't need anything special so this should do it:
date -d '1 hour ago' "+%H:00:00"
Why bother when you want exactly the hour where both %M and %S are expected to be zero?

Answer 4

You don't need date in this case; as seen below, built-in printf can generate formatted date-time strings too. Here -1 represents current time, and EPOCHSECONDS is a dynamic variable that expands to the number of seconds since epoch.
$ printf 'current hour is: %(%H)T:00:00\n' -1
current hour is: 17:00:00
$
$ printf 'next hour is: %(%H)T:00:00\n' $((EPOCHSECONDS + 3600))
next hour is: 18:00:00

Answer 5

Using awk,
$ awk ' BEGIN { st=systime();
print "current hour=" strftime("%F %H:00:00",st);
print "next hour=" strftime("%F %H:00:00",st+(60*60)) } '
current hour=2020-12-26 23:00:00
next hour=2020-12-27 00:00:00
$