Create timestamp variable in bash script

Question

I am trying to create a timestamp variable in a shell script to make the logging a little easier. I want to create the variable at the beginning of the script and have it print out the current time whenever I issue echo $timestamp. It proving to be more difficult then I thought. Here are some things I've tried:

timestamp="(date +"%T")" echo prints out (date +"%T")

timestamp="$(date +"%T")" echo prints the time when the variable was initialized.

Other things I've tried are just slight variations that didn't work any better. Does anyone know how to accomplish what I'm trying to do?

score 772 · Answer 1 · answered Nov 13 '13 at 13:01

772

If you want to get unix timestamp, then you need to use:

timestamp=$(date +%s)

%T will give you just the time; same as %H:%M:%S (via http://www.cyberciti.biz/faq/linux-unix-formatting-dates-for-display/)

answered Nov 13 '13 at 13:01

dchakarov

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But this variable will just hold the value of the time when the variable was initiated, am I right? – lindhe Aug 14 '14 at 23:04
18

I guess this is getting a lot of upvotes because it answers the title of the question, but it is not answering the question body : D OP wanted to get a different timestamp every time, whereas this will store one for the whole script. – fedorqui Apr 21 '16 at 06:23
3

I came here looking for this exactly. I.e. the proper format string to get a unix timestamp from `date`. However, I also upvoted the "correct" answer. I wasn't looking for that, but it's a better answer to the original question and it's also really useful to me. – vastlysuperiorman Mar 22 '19 at 17:24
Worked fine me after prepending 'shell` `timestamp=$(shell date +%s)` – Deepak Sharma Mar 08 '21 at 08:15
@fedorqui so what hinders op to just re-initialize the variable each time? – clockw0rk Aug 09 '22 at 10:57

score 424 · Accepted Answer · edited Sep 03 '20 at 05:18

424

In order to get the current timestamp and not the time of when a fixed variable is defined, the trick is to use a function and not a variable:

#!/bin/bash

# Define a timestamp function
timestamp() {
  date +"%T" # current time
}

# do something...
timestamp # print timestamp
# do something else...
timestamp # print another timestamp
# continue...

If you don't like the format given by the %T specifier you can combine the other time conversion specifiers accepted by date. For GNU date, you can find the complete list of these specifiers in the official documentation here: https://www.gnu.org/software/coreutils/manual/html_node/Time-conversion-specifiers.html#Time-conversion-specifiers

edited Sep 03 '20 at 05:18

Alishan Khan

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answered Jun 12 '13 at 13:06

giordano

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Depending on how you intend to use this, you'll still need to use command substitution: `echo "$(timestamp): something happened"`. – chepner Jun 12 '13 at 13:16
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As for formatting, here is a cut-and-dried set of most frequent formats: http://zxq9.com/archives/795 – zxq9 Nov 08 '14 at 16:38
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For me, I wanted `date +"%Y-%m-%d_%H-%M-%S"` – Kimball Robinson Dec 31 '14 at 17:57
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It would be nice to know why someone thinks this answer is wrong: 6 downvotes, but no one cared to explain why. By reading the question I really can't see what's wrong with the answer. – giordano Aug 20 '16 at 08:50
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for some reason this didn't give me the timestamp but the current time with ":" in between. – erikbstack Apr 13 '17 at 11:06
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I think a lot of people arrive at this question looking for a way to generate a unix timestamp (as I have) and find the answer by dchakarov to be more useful even though this answer better addresses the asker's question. – vastlysuperiorman Jun 16 '17 at 17:48
@erikbwork or whoever wants the unix timestamp just simply use `date +%s` – sorrow poetry May 04 '19 at 08:58
@KimballRobinson Instead of `%Y-%m-%d`, you can simply use `%F` – Nagabhushan S N Jun 08 '21 at 13:09

score 189 · Answer 3 · edited Dec 27 '22 at 06:36

You can refer to the following table to generate timestamps in various formats:

Format / result	Command	Output
YYYY-MM-DD	`date -I`	`$(date -I)`
YYYY-MM-DD_hh:mm:ss	`date +%F_%T`	`$(date +%F_%T)`
YYYYMMDD_hhmmss	`date +%Y%m%d_%H%M%S`	`$(date +%Y%m%d_%H%M%S)`
YYYYMMDD_hhmmss (UTC version)	`date --utc +%Y%m%d_%H%M%SZ`	`$(date --utc +%Y%m%d_%H%M%SZ)`
YYYYMMDD_hhmmss (with local TZ)	`date +%Y%m%d_%H%M%S%Z`	`$(date +%Y%m%d_%H%M%S%Z)`
YYYYMMSShhmmss	`date +%Y%m%d%H%M%S`	`$(date +%Y%m%d%H%M%S)`
YYYYMMSShhmmssnnnnnnnnn	`date +%Y%m%d%H%M%S%N`	`$(date +%Y%m%d%H%M%S%N)`
YYMMDD_hhmmss	`date +%y%m%d_%H%M%S`	`$(date +%y%m%d_%H%M%S)`
Seconds since UNIX epoch	`date +%s`	`$(date +%s)`
Nanoseconds only	`date +%N`	`$(date +%N)`
Nanoseconds since UNIX epoch	`date +%s%N`	`$(date +%s%N)`
ISO8601 UTC timestamp	`date --utc +%FT%TZ`	`$(date --utc +%FT%TZ)`
ISO8601 UTC timestamp + ms	`date --utc +%FT%T.%3NZ`	`$(date --utc +%FT%T.%3NZ)`
ISO8601 Local TZ timestamp	`date +%FT%T%Z`	`$(date +%FT%T%Z)`
YYYY-MM-DD (Short day)	`date +%F$%a$`	`$(date +%F$%a$)`
YYYY-MM-DD (Long day)	`date +%F$%A$`	`$(date +%F$%A$)`

Not often do I have to scroll through 11 other answers to find the best one. :) — Jason Wheeler, Oct 10 '21 at 00:21
Pay attention to`date -I`, it does not work on macos bash or zsh. Nevertheless very useful answer. — freedev, Oct 02 '22 at 21:50

score 113 · Answer 4 · edited Jul 23 '17 at 17:21

113

DATE=`date "+%Y%m%d"`

DATE_WITH_TIME=`date "+%Y%m%d-%H%M%S"` #add %3N as we want millisecond too

edited Jul 23 '17 at 17:21

Nam G VU

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answered Mar 30 '17 at 10:19

Girdhar Singh Rathore

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+1 for adding the millisecond part. This `echo $(date +"%Y-%m-%dT%T.%3N%z")` However I can't get it to work in a Mac terminal. How to do the same in Mac. Thanks – kosgeinsky Mar 18 '19 at 09:18
1

@kosgeinsky I installed GNU date via `brew install coreutils` and then use `gdate` instead of `date` – bhu Boue vidya May 03 '23 at 01:36

Caner · Answer 5 · 2019-11-25T13:12:35.360

81

ISO 8601 format (2018-12-23T12:34:56) is more readable than UNIX timestamp. However on some OSs you cannot have : in the filenames. Therefore I recommend using something like this instead:

2018-12-23_12-34-56

You can use the following command to get the timestamp in this format:

TIMESTAMP=`date +%Y-%m-%d_%H-%M-%S`

This is the format I have seen many applications use. Another nice thing about this is that if your file names start with this, you can sort them alphabetically and they would be sorted by date.

edited Nov 25 '19 at 13:12

answered Apr 10 '18 at 12:25

Caner

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`TZ=UTC date +...` can make this more portable by using UTC timestamp – MichaelChirico Dec 14 '19 at 10:16
Incorporating @MichaelChirico's comment and adding a *Zulu time* (== UTC) `Z` at the end; and modifying @Caner's to use `T`: `TIMESTAMP="$(TZ=UTC date +%Y-%m-%dT%H_%M_%SZ)"` – Abdull Dec 10 '21 at 11:30

Christoffer Nissen · Answer 6 · 2020-02-18T21:47:07.023

36

And for my fellow Europeans, try using this:

timestamp=$(date +%d-%m-%Y_%H-%M-%S)

will give a format of the format: "15-02-2020_19-21-58"

You call the variable and get the string representation like this

$timestamp

edited Feb 18 '20 at 21:47

answered Feb 15 '20 at 18:24

Christoffer Nissen

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Please consider using the code notation for your code. – sao Feb 15 '20 at 18:49
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or a universal solution: `date +%Y-%m-%d_%H-%M-%S` - and thank you for your answer. – edwardsmarkf Feb 07 '21 at 16:48
As a European, I've never used `DD-MM-YYYY` in my life, always `YYYY-MM-DD` for everything. That is different from writing "22nd June 2022" in a document, but numerically its never "22-06-2022", its always "2022-06-22". Just saying. – Kareem Aug 11 '22 at 10:30
Good for you :-) – Christoffer Nissen Aug 11 '22 at 11:56

Loïc · Answer 7 · 2023-05-27T13:04:23.730

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A lot of answers but I couldn't find what I was looking for :

date +"%s.%3N"

returns something like : 1606297368.210

edited May 27 '23 at 13:04

answered Nov 25 '20 at 11:26

Loïc

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On MacOS the built-in `date` doesn't support the `%N` format; see https://stackoverflow.com/a/33641565/1677912. – Mogsdad Aug 13 '21 at 17:15
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Yes, lots of answers, most of which are wrong because people apparently didn't read the question – giordano Aug 16 '21 at 16:14
1

This works and I wonder what's the meaning of symbol `N` – Jerry An Nov 19 '21 at 02:43
They say "Nanoseconds", makes sense: https://stackoverflow.com/a/69400542/3322400 – Loïc May 27 '23 at 13:02

score 21 · Answer 8 · answered Jun 12 '13 at 13:06

21

Use command substitution:

timestamp=$( date +%T )

answered Jun 12 '13 at 13:06

choroba

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This is what I already tried and it only prints out the time when the variable was initialized. – Dan Jun 12 '13 at 13:09
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@dan08: That's how variables work. Use a function if you want dynamic output. – choroba Jun 12 '13 at 13:09

score 19 · Answer 9 · answered Jan 27 '18 at 04:26

19

I am using ubuntu 14.04.

The correct way in my system should be date +%s.

The output of date +%T is like 12:25:25.

answered Jan 27 '18 at 04:26

Sean Lin

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Hem no: Under Ubuntu 14.04, bash is in version 4.3. [*Correct way should be* `printf -v varname '%(%s)T' -1`](https://stackoverflow.com/a/74938444/1765658) – F. Hauri - Give Up GitHub Apr 24 '23 at 16:32

score 15 · Answer 10 · edited Apr 20 '16 at 21:07

15

You can use

timestamp=`date --rfc-3339=seconds`

This delivers in the format 2014-02-01 15:12:35-05:00

The back-tick (`) characters will cause what is between them to be evaluated and have the result included in the line. date --help has other options.

edited Apr 20 '16 at 21:07

Adam Katz

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answered Feb 01 '14 at 20:16

Bill

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As for what time it gets, this should be executed immediately before inclusion in screen output or a log file intended to have the time of the output listed. – Bill Feb 01 '14 at 20:25
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this is less than ideal format for a timestamp because of the space in the output. Be sure to quote it "$timestamp" in usage or you will get two params to the command. e.g. `touch $timestamp` will produce two files. – harschware Apr 07 '17 at 16:12
1

For those wanting to customize this to remove the space, `date --rfc-3339=...` is (roughly?) equivalent to `date '+%F %T%:z'`, so removing the space is simply (eg): `date '+%F_%T%:z'` – michael Aug 29 '20 at 10:37

score 13 · Answer 11 · answered Jan 05 '19 at 17:43

Recent versions of bash don't require call to the external program date:

printf -v timestamp '%(%T)T'

%(...)T uses the corresponding argument as a UNIX timestamp, and formats it according to the strftime-style format between the parentheses. An argument of -1 corresponds to the current time, and when no ambiguity would occur can be omitted.

score 5 · Answer 12 · answered Dec 28 '16 at 02:15

5

timestamp=$(awk 'BEGIN {srand(); print srand()}')

srand without a value uses the current timestamp with most Awk implementations.

answered Dec 28 '16 at 02:15

Zombo

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fwiw, being curious about the performance: the following print the same: (1) `awk '....'` (as shown above); (2) `date '+%s'`; (3) `printf '%(%s)T'`; listed in order of increasing performance: on my system, `date` is roughly 2x faster than `awk`; and `printf` is over 50x faster than `date` & 100x faster than `awk`. – michael Aug 29 '20 at 10:32

F. Hauri - Give Up GitHub · Answer 13 · 2023-08-24T19:47:50.443

`bash` can show time in microseconds natively!

1. Avoid forks!!!

Having to run date for each logged line is overkill!!

Prefer to use bash's builtins whenever possible.

At time this question was asked, bash version was bash-4.2.

In this version, the pure bash way for printing current time is:

printf '%(%T)T\n' -1

or

printf '%(%T)T\n' -1

So a short function login each lines with timestamp could be:

logLine() {
    printf '%(%T)T %s\n' -1 "$*"
}

Then

$ logLine Hello world.
10:11:32 Hello world.

2. Time in seconds, using `printf` builtin:

For storing current time into a variable, you will use:

printf -v varname '%(%T)T' -1

or to store (reusable) UNIX EPOCH:

printf -v varname '%(%s)T' -1

Then

printf 'Stored time stamp is: %(%c)T\n' "$varname"
Stored time stamp is: Sat Jan 27 04:26:00 2018

2.1 Time in seconds, using `$EPOCHSECONDS` pseudo variable

From version 5.0-alpha of bash, (2018-05-22) we could use two pseudo variables: $EPOCHSECONDS and $EPOCHREALTIME:

man -P'less +/EPOCH' bash

EPOCHREALTIME
       Each time this parameter is referenced, it expands to the number
       of  seconds  since  the  Unix  Epoch (see time(3)) as a floating
       point  value  with  micro-second  granularity.   Assignments  to
       EPOCHREALTIME  are ignored.  If EPOCHREALTIME is unset, it loses
       its special properties, even if it is subsequently reset.
EPOCHSECONDS
       Each time this parameter is referenced, it expands to the number
       of  seconds  since the Unix Epoch (see time(3)).  Assignments to
       EPOCHSECONDS are ignored.  If EPOCHSECONDS is  unset,  it  loses
       its special properties, even if it is subsequently reset.

echo $EPOCHSECONDS
1692818546
myvar=$EPOCHSECONDS
echo $myvar
1692818547

Sample: Sleep until next minute

sleep $((60-EPOCHSECONDS%60));printf '%(%T)T\n' -1
21:26:00

3. About microseconds

Today, I use bash >= 5.1.4...

From version 5.0-alpha of bash, (2018-05-22):

b. There is an EPOCHSECONDS variable, which expands to the time in seconds since the Unix epoch.

c. There is an EPOCHREALTIME variable, which expands to the time in seconds since the Unix epoch with microsecond granularity.

So if you want to use microsecond granularity, function could become:

logLine() {
    local now=$EPOCHREALTIME
    printf '%(%T)T.%s %s\n' ${now%.*} ${now#*.} "$*"
}

Then

$ logLine Hello world.
10:15:56.862732 Hello world.

Sleep until next minute become a little more complex as bash can't compute real numbers:

slptim=00000$((60000000-${EPOCHREALTIME/.}%60000000));\
  printf -v slptim %.6f ${slptim::-6}.${slptim: -6};\
  sleep $slptim;\
  now=${EPOCHREALTIME};\
  printf '%(%H:%M)T:%06.3f\n' ${now%.*} $((${now%.*}%60)).${now#*.}
21:44:00.001

Important: But care! _both variables are not expanded in same way!! See: Don't mix EPOCHREALTIME and EPOCHSECONDS!!!

score 3 · Answer 14 · answered Sep 27 '22 at 15:26

3

You can do this with following comands.

For timestamp with seconds: checkDate=$(date "+%s")

For formated date: checkDate=$(date "+%Y-%m-%d %H:%M:%S")

answered Sep 27 '22 at 15:26

andranikasl

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Jonathan L · Answer 15 · 2023-01-09T07:31:32.817

A timestamp formatting trick for GNU bash, version 4.4.20(1)-release (x86_64-pc-linux-gnu)

 echo "$(date +%Y-%m-%d_%H:%M:%S.%6N) Info >>> enter main"

output:

 2023-01-08_23:08:48.013592 Info >>> enter main

If you want to replace '_' with a space, do the following (w/o '\' got error message)

 echo "$(date +%Y-%m-%d\ %H:%M:%S.%6N) Info >>> enter main"
 echo "$(date +%Y-%m-%d\ %T.%6N) Info >>> enter main"

output:

 2023-01-08 23:10:40.692674 Info >>> enter main

carloswm85 · Answer 16 · 2021-08-12T23:36:06.820

This is a little more than you asked, so you can customize it to your needs.

I am trying to create a timestamp variable in a shell script...

This script will allow you to create a variable. Though I'm not entirely sure how reusable is when changing the shell context. But it will do the job.

function timestamp {
    TEXT="Date:"
    DATE=`date +%Y-%m-%d`
    TIME=`date +%H:%M:%S`
    ZONE=`date +"%Z %z"`
    echo $TEXT $DATE $TIME $ZONE
}

function fulldate {
  timevariable=$(timestamp)
  echo $timevariable
}

echo "- Output 1:"
timestamp
echo "- Output 2:"
fulldate
echo "- Output 3:"
echo $timevariable

Outputs:

- Output 1:
Date: 2021-08-12 23:28:08 UTC +0000
- Output 2:
Date: 2021-08-12 23:28:08 UTC +0000
- Output 3:
Date: 2021-08-12 23:28:08 UTC +0000

I've tested this working on GNU bash, version 4.4.23(1)-release (x86_64-pc-msys)

pamphlet · Answer 17 · 2021-12-28T22:58:11.680

If performance is a concern, @chepner's answer is a clear winner.

With a bit more complexity, you can also get micro- or milli- second granularity using only bash built-ins. Below is an example of a function that emits the current timestamp including milliseconds:

timestamp() {
    IFS=. read S US <<<$EPOCHREALTIME # Read epoch seconds/microseconds
    MS=$((10#$US/1000)) # Convert to milliseconds (interpret in base-10, even with leading 0)
    printf '%(%F %T)T.%03i' $S $MS # Emit formatted timestamp
}

TS=$(timestamp) # Invoke function, assign to variable

Note that the printf format can be adjusted emit your preferred date/time format.

score 0 · Answer 18 · answered Jun 03 '22 at 17:49

The following will give local date and time - it does require internet access however. Depending on what is being logged, this could be beneficial - monitoring and logging connection status?

curl -i --silent https://google.com/ 2>&1 | grep date

date: Fri, 03 Jun 2022 17:39:19 GMT

Create timestamp variable in bash script

18 Answers18

`bash` can show time in microseconds natively!

1. Avoid forks!!!

2. Time in seconds, using `printf` builtin:

2.1 Time in seconds, using `$EPOCHSECONDS` pseudo variable

3. About microseconds

Linked

Create timestamp variable in bash script

18 Answers18

bash can show time in microseconds natively!

1. Avoid forks!!!

2. Time in seconds, using printf builtin:

2.1 Time in seconds, using $EPOCHSECONDS pseudo variable

3. About microseconds

Linked

`bash` can show time in microseconds natively!

2. Time in seconds, using `printf` builtin:

2.1 Time in seconds, using `$EPOCHSECONDS` pseudo variable