date: get current 15 minute interval

Question

Is there any way I can get the current 15 minute interval using the date command or similar ?

e.g. something like date %Y.%m.%d %H:%M will give me 2011.02.22 10:19 , I need something that yields 2011.02.22 10:15 in the time span from 10:15 to 10:29.

Answer 1

You can get the current unix timestamp with date "+%s", find the current quarter-hour with some simple math (my example is in bash) and print it back with a better format with date :

curdate=`date "+%s"`
curquarter=$(($curdate - ($curdate % (15 * 60))))
date -d"@$curquarter"

The @ syntax to set the current date and time from a timestamp is a GNU extention to date, if it don't works on your OS, you can do the same like this (don't forget to specify UTC, otherwise, it won't work) :

date -d"1970-01-01 $curquarter seconds UTC"

Answer 2

The following methods make it unnecessary to call date twice.
A system call's overhead can make a "simple" command 100 times slower than bash doing the same thing in its own local environment.

UPDATE Just a quick mention about my above comment: "100 times slower". It can now read "500 times slower"... I recently fell (no, walked blindly) into this very issue. here is the link: Fast way to build a test file

eval $(date +Y=%Y\;m=%m\;d=%d\;H=%H\;M=%M)
[[ "$M" < "15" ]] && M=00 # cater for octal clash
M=$(((M/15)*15))
((M==0)) && M=00 # the math returns 0, so make it 00  
echo $Y.$m.$d $H:$M  

or

eval $(date +Y=%Y\;m=%m\;d=%d\;H=%H\;M=%M)
if   [[ "$M" < "15" ]] ; then M=00
elif [[ "$M" < "30" ]] ; then M=15
elif [[ "$M" < "45" ]] ; then M=30
else M=45
fi
echo $Y.$m.$d $H:$M

Both versions will return only

2011.02.23 01:00
2011.02.23 01:15
2011.02.23 01:30
2011.02.23 01:45   

---

Here is the first one with a TEST loop for all 60 values {00..59}

for X in {00..59} ;                         ###### TEST
do                                          ###### TEST 
  eval $(date +Y=%Y\;m=%m\;d=%d\;H=%H\;M=%M)
  M=$X                                      ###### TEST 
  [[ "$M" < "15" ]] && M=00 # cater for octal clash
  M=$(((M/15)*15))
  ((M==0)) && M=00 # the math returns 0, so make it 00  
  echo $Y.$m.$d $H:$M 
done                                        ###### TEST 

Answer 3

Here's a way to work on dates in the shell. First call date to get the components, and fill the positional parameters ($1, $2, etc) with the components (note that this is one of these rare cases where you do want to use $(…) outside of double quotes, to break the string into words). Then perform arithmetics, tests, or whatever you need to do on the components. Finally assemble the components.

The arithmetic part can be a little tricky because shells treat 0 as an octal prefix; for example here $(($5/15)) would fail at 8 or 9 minutes past the hour. Since there's at most one leading 0, ${5#0} is safe for arithmetic. Adding 100 and subsequently stripping the 1 is a way to get a fixed number of digits in the output.

set $(date "+%Y %m %d %H %M")
m=$((100+15*(${5#0}/15)))
last_quarter_hour="$1.$2.$3 $4:${m#1}"

Answer 4

Maybe it doesn't matter anymore but you could try my very own dateutils. Rounding (down) to minutes is done with dround and a negative argument:

dround now /-15m
=>
  2012-07-11T13:00:00

Or to adhere to your format:

dround now /-15m -f '%Y.%m.%d %H:%M'
=>
  2012.07.11 13:00

Answer 5

Some shells are able to do the work without calling an external date command:

ksh a=$(printf '%(%s)T\n'); printf '%(%Y.%m.%d %H:%M)T\n' "#$((a-a%(15*60)))"
bash a=$(printf '%(%s)T\n'); printf '%(%Y.%m.%d %H:%M)T\n' "$((a-a%(15*60)))"
zsh zmodload zsh/datetime; a=$EPOCHSECONDS; strftime '%Y-%m-%d %H:%M' $((a-a%(15*60)))

The three above provide local (not UTC) time. Use a leading TZ=UTC0 if needed.

The ksh and bash syntax is almost identical (except for the required # in ksh). The zsh require to load a module (included with the zsh distribution).

It is also possible to do it with (GNU) awk:

gawk awk 'BEGIN{t=systime();print strftime("%Y.%m.%d %H:%M",t-t%(15*60),1)}'

This provide an UTC result (change the last 1 to 0) if local is needed. But loading an external awk or an external zsh module might be as slow as calling date itself:

gnu-date a=$(date +%s); date -ud "@$((a-a%(15*60)))" +'%Y.%m.%d %H:%M'

A small executable like busybox could provide similar results:

busybox-date a=$(busybox date +%s);busybox date -ud "@$((a-a%(15*60)))" +'%Y.%m.%d %H:%M'

Note that the leading busybox word may be omitted if busybox is linked to those names in a directory of the PATH.

Both date and busybox date above will print UTC times. Remove the -u option for local times.

---

If your OS has a more limited version of date (and that is what you must use) then try:

a=$(date +%s); a=$(( a-a%(15*60) ))
date -d"1970-01-01 $a seconds UTC" +'%Y.%m.%d %H:%M'

Or, if in FreeBSD, try:

a=$(date +%s); a=$(( a-a%(15*60) ))
date -r "$a" +'%Y.%m.%d %H:%M'

Answer 6

If you can live with calling date two times, this one works in bash on Solaris:

date +"%Y.%m.%d %H:$(( $(date +'%M') / 15 * 15 ))"

Edited on behalf of the comment to:

date +"%Y.%m.%d %H:$(( $(date +'%M') / 15 * 15 ))" | sed 's/:0$/:00/'

Answer 7

Am not sure about your exact requirement. However, if you want to generate the time after 15 min, then you can use something like date -d '+15 min'. Output is shown below:

$ date; date  -d '+15 min'
Tue Feb 22 18:12:39 IST 2011
Tue Feb 22 18:27:39 IST 2011