Linux date command, finding seconds to next hour - linux

Question

How do I find the seconds to the next hour using date? I know I can do
date -d "next hour"
but that just adds 1 hour to the present time. I want it to show the seconds to the next full hour. For example if the current time is 9:39am I want to find the number of seconds to 10am

Answer 1

The epoch timestamp of right now is
now=$(date '+%s')
That of the next hour is
next=$(date -d $(date -d 'next hour' '+%H:00:00') '+%s')
The number of seconds until the next hour is
echo $(( next - now ))
For a continuous solution, use functions:
now() { date +%s; }
next() { date -d $(date -d "next ${1- hour}" '+%H:00:00') '+%s'; }
And now you have
echo $(( $(next) - $(now) ))
and even
echo $(( $(next day) - $(now) ))
Another way
Another slightly mathier approach still uses the epoch timestamp. We know it started on an hour, so the timestamp mod 3600 only equals zero on the hour. Thus
$(( $(date +%s) % 3600 ))
is the number of seconds since the last hour, and
$(( 3600 - $(date +%s) % 3600 ))
is the number of seconds until the next.

Answer 2

Well, there's always the straightforward mathy way:
read min sec <<<$(date +'%M %S')
echo $(( 3600 - 10#$min*60 - 10#$sec ))
EDIT: removed race condition, added explicit radix. Thanks, #rici and #gniourf_gniourf.

Answer 3

With Bash≥4.2 you can use printf with the %(...)T modifier to access dates (current date corresponds to argument -1, or empty since version 4.3):
printf -v left '%(3600-60*10#%M-10#%S)T' -1
echo "$((left))"
Pure Bash and no subshells!
The 10# is here to ensure that Bash's arithmetic (expanded in the $((...))) treats the following number in radix 10. Without this, you'd get an error if the minute or second is 08 or 09.

Answer 4

Try doing this :
LANG=C
now=$(date +%s)
next="$(date |
perl -pe 's/(\d{2}):\d{2}:\d{2}/sprintf "%.2d:00:00", $1 + 1/e')"
next=$(date -d "$next" +%s)
echo $(( next - now ))
OUTPUT :
2422

Answer 5

#!/usr/bin/env bash
is=`date +%S`
im=`date +%M`
echo $((((60-$im)*60)+(60-$is)))