withintest.sh

#!/bin/bash

# Check if the current time falls within defined time range on UNIX

#set -e
set -o pipefail
function errtrap {     es=$?;     echo "ERROR line $1: Command exited with status $es.">&2; exit 1; }; trap 'errtrap $LINENO' ERR

#export TZ=Asia/Kolkata

within() { (
  set +x
  set -e
  
  #export TZ=Asia/Kolkata
  
  beg=${1:?}
  end=${2:?}
  
  if [ -z "$3" ]; then
    now=`date +%s`
  else
    now=`date +%s -d "$3"`
  fi
  
  today=`date +%F -d@${now:?}`

  if ! end1=`date +%s -d"${today:?} ${end:?}" 2>/dev/null`; then
    tomorrow=`date +%F -d"${today:?} 1 days"`
    end1=`date +%s -d"${tomorrow:?} ${end:?} 1 days ago"`
    end2=`date +%s -d"${tomorrow:?} ${end:?}"`
  else
    end2=`date +%s -u -d "1970-01-01 $end1 seconds 1 days"`
  fi

  if ! beg2=`date +%s -d"${today:?} ${beg:?}" 2>/dev/null`; then
    yesterday=`date +%F -d"${today:?} 1 days ago"`
    beg2=`date +%s -d"${yesterday:?} ${beg:?} 1 days"`
  fi

  if ((beg2 < end1)); then
    beg1=$beg2
  else
    beg1=`date +%s -u -d "1970-01-01 $beg2 seconds 1 days ago"`
  fi

  realbeg=$(( now >= beg2 ? beg2 : beg1 ))
  
  realend=$(( realbeg > end1 ? end2 : end1 ))
  
  if (( now >= realbeg && now < realend )); then
    echo "Exiting because `date --iso-8601=seconds -d@$realbeg` <= `date --iso-8601=seconds -d@$now` < `date --iso-8601=seconds -d@$realend`"
    exit 1
  fi
  exit 0

)}

t() {
  within "$@"
}

f() {
! t "$@"
}

export TZ=Europe/Berlin

t "02:01" "02:03" "2020-03-29T05:01"
f "02:01" "02:03" "2020-03-30T02:02"

#set -x
export TZ=Asia/Kolkata

f 23:00 06:30 03:00
t 23:00 06:30 13:00

f "0:01 IST" "0:00 IST" "2020-07-19 0:01 IST"
f "13:01 IST" "13:00 IST" "2020-07-19 0:01 IST"

f "0:01 IST" "0:00 IST" "2020-07-19 0:01 IST"
f "0:01 IST" "0:00 IST" "2020-07-19 0:02 IST"
f "0:01 IST" "0:00 IST" "2020-07-19 23:59 IST"
t "0:01 IST" "0:00 IST" "2020-07-19 0:00 IST"

t "11:30PM IST" "2:30AM IST" "2020-07-19 23:29 IST"
f "11:30PM IST" "2:30AM IST" "2020-07-19 23:30 IST"
f "11:30PM IST" "2:30AM IST" "2020-07-19 0:00 IST"
f "11:30PM IST" "2:30AM IST" "2020-07-19 2:29 IST"
t "11:30PM IST" "2:30AM IST" "2020-07-19 2:30 IST"

t "11:30PM IST" "11:40PM IST" "2020-07-19 23:29 IST"
f "11:30PM IST" "11:40PM IST" "2020-07-19 23:30 IST"
f "11:30PM IST" "11:40PM IST" "2020-07-19 23:39 IST"
t "11:30PM IST" "11:40PM IST" "2020-07-19 23:40 IST"

echo ok