18

Using the date program, how can I calculate the number of seconds since midnight?

jasonwryan
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Ducky
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4 Answers4

24

To avoid race conditions, still assuming GNU date:

eval "$(date +'today=%F now=%s')"
midnight=$(date -d "$today 0" +%s)
echo "$((now - midnight))"

With zsh, you can do it internally:

zmodload zsh/datetime
now=$EPOCHSECONDS
strftime -s today %F $now
strftime -rs midnight %F $today
echo $((now - midnight))

Portably, in timezones where there's no daylight saving switch, you could do:

eval "$(date +'h=%H m=%M s=%S')"
echo "$((${h#0} * 3600 + ${m#0} * 60 
+ ${s#0}))"

The ${X#0} is to strip one leading 0 which in some shells like bash, dash and posh cause problems with 08 and 09 (where the shell complains about it being an invalid octal number).

Stéphane Chazelas
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15

There is no need for any arithmetic expression, just use pure date:

date -d "1970-01-01 UTC $(date +%T)" +%s
Ipor Sircer
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    Great answer, should be the top one. – Leopoldo Sanczyk Mar 28 '19 at 19:02
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    On Mac brew install coreutils and replace date with gdate – Connor McCormick Aug 12 '19 at 20:48
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    In timezones with daylight saving time, that gives incorrect results 2 days per year. For instance, in the UK at 2am on 2020-10-25 (the last Sunday in October), which is 3 hours after midnight as there have been a time change at 1am earlier, it gives 7200 instead of 10800. – Stéphane Chazelas Jun 28 '20 at 06:45
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    Actually, arithmetic expressions can be much faster than shelling out to external command twice. There are other ways to do the job, with calling date only once. –  Mar 10 '21 at 23:15
2

Based on bash, get current time in milliseconds since midnight, on a GNU system, it can be done like this:

$ now=$(date '+%s')
$ midnight=$(date -d 'today 00:00:00' '+%s')
$ echo $(( now - midnight ))
53983
Community
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fedorqui
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1

Seconds since midnight?

For Bash (with GNU date) here are two one-liners which work equally well:

echo $(( - $(date -d 0 +%s) + EPOCHSECONDS ))

or

echo $(( $(date '+%-H *3600 + %-M *60 + %-S') ))

Either one works just as well.

Similarly, I find it useful to have a function for minutes since midnight:

minutes () { echo $(( $(date '+%-H *60 + %-M') )) ;}
Pourko
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