What you're looking for is date --date='06/12/2012 07:21:22' +"%s". Keep in mind that this assumes you're using GNU coreutils, as both --date and the %s format string are GNU extensions. POSIX doesn't specify either of those, so there is no portable way of making such conversion even on POSIX compliant systems.

Consult the appropriate manual page for other versions of date.

Note: bash --date and -d option expects the date in US or ISO8601 format, i.e. mm/dd/yyyy or yyyy-mm-dd, not in UK, EU, or any other format.

For Linux, run this command:

date -d '06/12/2012 07:21:22' +"%s"

For macOS, run this command:

date -jf "%Y-%m-%d %H:%M:%S" "1970-01-01 00:00:00" +%s

A lot of these answers are overly complicated and also are missing how to use variables. This is how you would do it more simply on standard Linux system (as previously mentioned the date command would have to be adjusted for Mac Users) :

Sample script:

#!/bin/bash
orig="Apr 28 07:50:01"
epoch=$(date -d "${orig}" +"%s")
epoch_to_date=$(date -d @$epoch +%Y%m%d_%H%M%S)    

echo "RESULTS:"
echo "original = $orig"
echo "epoch conv = $epoch"
echo "epoch to human readable time stamp = $epoch_to_date"

Results in :

RESULTS:
original = Apr 28 07:50:01
epoch conv = 1524916201 
epoch to human readable time stamp = 20180428_075001

Or as a function :

# -- Converts from human to epoch or epoch to human, specifically "Apr 28 07:50:01" human.
#    typeset now=$(date +"%s")
#    typeset now_human_date=$(convert_cron_time "human" "$now")

function convert_cron_time() {
    case "${1,,}" in
        epoch)
            # human to epoch (eg. "Apr 28 07:50:01" to 1524916201)
            echo $(date -d "${2}" +"%s")
            ;;
        human)
            # epoch to human (eg. 1524916201 to "Apr 28 07:50:01")
            echo $(date -d "@${2}" +"%b %d %H:%M:%S")
            ;;
    esac
}

Just be sure what timezone you want to use.

datetime="06/12/2012 07:21:22"

Most popular use takes machine timezone.

date -d "$datetime" +"%s" #depends on local timezone, my output = "1339456882"

But in case you intentionally want to pass UTC datetime and you want proper timezone you need to add -u flag. Otherwise you convert it from your local timezone.

date -u -d "$datetime" +"%s" #general output = "1339485682"

Efficient way to convert date time string to epoch in bash

Avoiding useless repetitives forks, in order to make this translation a lot quicker...

Instead of running 1 fork for each translation, we could run date -f - +%s as background process...

Intro

Common syntax:

epochDate=$(date -d "$InputDate" +%s)

Work fine, but become heavy if run repetetively!

In this post, you will find

• a Quick Demo, following this,
• some Explanations,
• a Function useable for many Un*x tools (bc, rot13, sed...).

Quick Demo using coproc

coproc DATE { exec stdbuf -o0 /bin/date -f - +%s 2>&1 ;}
echo  >&${DATE[1]}  06/12/2012 07:21:22
read -ru${DATE[0]}  epochDate
printf 'EPOCH: %u  Date:%(%c)T\n' $epochDate $epochDate

EPOCH: 1339478482  Date:Tue Jun 12 07:21:22 2012

About performances, you could compare:

time for i in {1..900};do echo >&${DATE[1]} "now";read -ru${DATE[0]} ans;done
real    0m0.029s
user    0m0.018s
sys     0m0.005s

and:

time for i in {1..900};do ans=$(date +%s -d "now");done 
real    0m1.465s
user    0m0.962s
sys     0m0.442s

From more than 1.4 seconds to less than 30 milliseconds!!(on my host).

You could check echo $ans, replace "now" by "2019-25-12 20:10:00" and so on...

Little function

myDate() { 
    if [[ $1 == -v ]]; then
        local -n out=$2
        shift 2
    else
        local out
    fi
    echo "$*" >&${DATE[1]}
    read -ru ${DATE[0]} out
    [[ ${out@A} == out=* ]] && echo $out
    case $out in ''|*[!0-9]*) return 1;; esac
}

myDate 06/12/2012 07:21:22

1339478482

myDate -v var 06/12/2012 07:21:22
printf '%(%c)T\n' $var

Tue Jun 12 07:21:22 2012

myDate -v var wrong string
printf 'ResultCode: %d: Var: "%s"\n' "$?" "$var"

ResultCode: 1: Var: "/bin/date: invalid date 'wrong string'"

Stop background

You could, once requirement of date subprocess ended:

kill ${DATE_PID}
exec {DATE[1]}>&- ; exec {DATE[0]}<&-

[1]+  Terminated              coproc DATE { exec stdbuf -o0 /bin/date -f - +%s; }

Original post (detailed explanation)

Instead of running 1 fork by date to convert, run date just 1 time and do all convertion with same process (this could become a lot quicker)!:

date -f - +%s <<eof
Apr 17  2014
May 21  2012
Mar  8 00:07
Feb 11 00:09
eof
1397685600
1337551200
1520464020
1518304140

Sample:

start1=$(LANG=C ps ho lstart 1)
start2=$(LANG=C ps ho lstart $$)
dirchg=$(LANG=C date -r .)
read -p "A date: " userdate
{ read start1 ; read start2 ; read dirchg ; read userdate ;} < <(
   date -f - +%s <<<"$start1"$'\n'"$start2"$'\n'"$dirchg"$'\n'"$userdate" )

Then now have a look:

declare -p start1 start2 dirchg userdate

(may answer something like:

declare -- start1="1518549549"
declare -- start2="1520183716"
declare -- dirchg="1520601919"
declare -- userdate="1397685600"

This was done in only one date subprocess execution!

Using long running subprocess

We just need one fifo:

mkfifo /tmp/myDateFifo
exec 7> >(exec stdbuf -o0 /bin/date -f - +%s >/tmp/myDateFifo)
exec 8</tmp/myDateFifo
rm /tmp/myDateFifo

(Note: As process is running and all descriptors are opened, we could safely remove fifo's filesystem entry.)

Then now:

LANG=C ps ho lstart 1 $$ >&7
read -u 8 start1
read -u 8 start2
LANG=C date -r . >&7
read -u 8 dirchg

read -p "Some date: " userdate
echo >&7 $userdate
read -u 8 userdate

We could buid a little function:

mydate() {
    local var=$1;
    shift;
    echo >&7 $@
    read -u 8 $var
}

mydate start1 $(LANG=C ps ho lstart 1)
echo $start1

Or use my newConnector function

With functions for connecting MySQL/MariaDB, PostgreSQL and SQLite...

You may find them in different version on GitHub, or on my site: download or show.

wget https://raw.githubusercontent.com/F-Hauri/Connector-bash/master/shell_connector.bash

wget http://f-hauri.ch/vrac/shell_connector.sh
. shell_connector.bash 
newConnector /bin/date '-f - +%s' @0 0

myDate "2018-1-1 12:00" test
echo $test
1514804400

Nota: On GitHub, functions and test are separated files. On my site test are run simply if this script is not sourced. On GitHub, there is no upgrade anymore! Last verified version is on my site!

# Exit here if script is sourced
[ "$0" = "$BASH_SOURCE" ] || { true;return 0;}

get_curr_date () {
    # get unix time
    DATE=$(date +%s)
    echo "DATE_CURR : "$DATE
}

conv_utime_hread () {
    # convert unix time to human readable format
    DATE_HREAD=$(date -d @$DATE +%Y%m%d_%H%M%S)
    echo "DATE_HREAD          : "$DATE_HREAD
}

I added the following alias to .bashrc (or .zshrc) - note the --utc switch which converts the input as UTC time zone. You can remove it to use the local machine time zone but in my experience I usually want UTC for this:

alias datetoepoch='date --utc +%s -d'

Now I can just type in the terminal something like:

datetoepoch 2024-03-18

and get the result:

1710720000

Not exactly asked for, but I use this to convert an OpenLDAP timestamp like 20241111073923Z to seconds since the epoch:

echo $(date -u --date=$(echo "$1" | sed \
-e 's/^\(....\)\(..\)\(..\)\(..\)\(..\)\(..\)Z$/\1-\2-\3T\4:\5:\6/') '+%s')

For the example timestamp the command executed will be date -u --date=2024-11-11T07:39:23 +%s, and the output will be 1731310763.

A bash function is always faster than exec date, here is the code I used to convert datetime to epoch seconds for computing seconds difference between datetimes. However the timezone is ignored, so it's not exactly epoch seconds. While it could be easy to add timezone offset seconds.

        if [ "${datetime/ /}" != "$datetime" ]; then
            date="${datetime% *}"
            time="${datetime##* }"
        else
            date="${datetime%-*}"
            time="${datetime##*-}"
        fi

        if [ "${date/-/}" != "$date" ]; then
            year="${date%%-*}"
            s="${date#*-}"
            month=$(( 1"${s%%-*}" - 100 ))
            day=$((   1"${s#*-}"  - 100 ))
        else
            year=${date:0:4}
            month=$((  1"${date:4:2}" - 100 ))
            day=$((    1"${date:6:2}" - 100 ))
        fi
        
        if [ "${time/:/}" != "$time" ]; then
            hour=${time%%:*}
            s=${time#*:}
            minute=$(( 1"${s%%:*}" - 100 ))
            second=$(( 1"${s#*:}"  - 100 ))
        else
            hour=$((   1"${time:0:2}" - 100 ))
            minute=$(( 1"${time:2:2}" - 100 ))
            second=$(( 1"${time:4:2}" - 100 ))
        fi
        
        month0=$(( month - 1 ))
        day0=$(( day - 1 ))

        if [ $((year % 100)) == 0 ]; then
            leap=$(( year % 400 == 0 ))
        else
            leap=$(( year % 4 == 0 ))
        fi
        
        if [ $leap == 1 ]; then
            mo=(31 29 31 30 31 30 31 31 30 31 30 31)
            mobase=(0 31 60 91 121 152 182 213 244 274 305 335)
        else
            mo=(31 28 31 30 31 30 31 31 30 31 30 31)
            mobase=(0 31 59 90 120 151 181 212 243 273 304 334)
        fi

        days_1970=$(( 1970 * 365 + 1970 / 4 - 1970 / 100 + 1970 / 400 ))
        days_0=$(( year * 365 + year / 4 - year / 100 + year / 400 ))
        epochday=$(( days_0 - days_1970 + mobase[month0] + day0 ))
        epochsec=$(( epochday * 86400 + (hour * 60 + minute) * 60 + second ))