How to convert from day of year and year to a date YYYYMMDD?

Question

I'm looking to go from day of year (1-366) and year (e.g. 2011) to a date in the format YYYYMMDD?

Answer 1

This Bash function works for me on a GNU-based system:

jul () { date -d "$1-01-01 +$2 days -1 day" "+%Y%m%d"; }

Some examples:

$ y=2011; od=0; for d in {-4..4} 59 60 {364..366} 425 426; do (( d > od + 1)) && echo; printf "%3s " $d; jul $y $d; od=$d; done
 -4 20101227
 -3 20101228
 -2 20101229
 -1 20101230
  0 20101231
  1 20110101
  2 20110102
  3 20110103
  4 20110104

 59 20110228
 60 20110301

364 20111230
365 20111231
366 20120101

425 20120229
426 20120301

This function considers Julian day zero to be the last day of the previous year.

And here is a bash function for UNIX-based systems, such as macOS:

jul () { (( $2 >=0 )) && local pre=+; date -v$pre$2d -v-1d -j -f "%Y-%m-%d" $1-01-01 +%Y%m%d; }

Answer 2

Can't be done in just Bash, but if you have Perl:

use POSIX;

my ($jday, $year) = (100, 2011);

# Unix time in seconds since Jan 1st 1970
my $time = mktime(0,0,0, $jday, 0, $year-1900);

# same thing as a list that we can use for date/time formatting
my @tm = localtime $time;

my $yyyymmdd = strftime "%Y%m%d", @tm;

Answer 3

Run info 'Date input formats' to see what formats are allowed.

The YYYY-DDD date format does not seem to be there, and trying

$ date -d '2011-011'
date: invalid date `2011-011'

shows it doesn't work, so I think njd is correct, the best way is to use an external tool other than bash and date.

If you really want to use only bash and basic command line tools, you could do something like this:

julian_date_to_yyyymmdd()
{
    date=$1    # assume all dates are in YYYYMMM format
    year=${date%???}
    jday=${date#$year}
    for m in `seq 1 12`; do
        for d in `seq 1 31`; do
            yyyymmdd=$(printf "%d%02d%02d" $year $m $d)
            j=$(date +"%j" -d "$yyyymmdd" 2>/dev/null)
            if test "$jday" = "$j"; then
                echo "$yyyymmdd"
                return 0
            fi
        done
    done
    echo "Invalid date" >&2
    return 1
}

But that's a pretty slow way to do it.

A faster but more complex way tries to loop over each month, finds the last day in that month, then sees if the Julian day is in that range.

# year_month_day_to_jday <year> <month> <day> => <jday>
# returns 0 if date is valid, non-zero otherwise
# year_month_day_to_jday 2011 2 1 => 32
# year_month_day_to_jday 2011 1 32 => error
year_month_day_to_jday()
{
    # XXX use local or typeset if your shell supports it
    _s=$(printf "%d%02d%02d" "$1" "$2" "$3")
    date +"%j" -d "$_s"
}

# last_day_of_month_jday <year> <month>
# last_day_of_month_jday 2011 2 => 59
last_day_of_month_jday()
{
    # XXX use local or typeset if you have it
    _year=$1
    _month=$2
    _day=31

    # GNU date exits with 0 if day is valid, non-0 if invalid
    # try counting down from 31 until we find the first valid date
    while test $_day -gt 0; do
        if _jday=$(year_month_day_to_jday $_year $_month $_day 2>/dev/null); then
            echo "$_jday"
            return 0
        fi
        _day=$((_day - 1))
    done
    echo "Invalid date" >&2
    return 1
}

# first_day_of_month_jday <year> <month>
# first_day_of_month_jday 2011 2 => 32
first_day_of_month_jday()
{
    # XXX use local or typeset if you have it
    _year=$1
    _month=$2
    _day=1

    if _jday=$(year_month_day_to_jday $_year $_month 1); then
        echo "$_jday"
        return 0
    else
        echo "Invalid date" >&2
        return 1
    fi
}

# julian_date_to_yyyymmdd <julian day> <4-digit year>
# e.g. julian_date_to_yyyymmdd 32 2011 => 20110201
julian_date_to_yyyymmdd()
{
    jday=$1
    year=$2

    for m in $(seq 1 12); do
        endjday=$(last_day_of_month_jday $year $m)
        if test $jday -le $endjday; then
            startjday=$(first_day_of_month_jday $year $m)
            d=$((jday - startjday + 1))
            printf "%d%02d%02d\n" $year $m $d
            return 0
        fi
    done
    echo "Invalid date" >&2
    return 1
}

Answer 4

If day of year (1-366) is 149 and year is 2014,

$ date -d "148 days 2014-01-01" +"%Y%m%d"
20140529

Be sure to input the day of year -1 value.

Answer 5

On a POSIX terminal:

jul () { date -v$1y -v1m -v1d -v+$2d -v-1d "+%Y%m%d"; }

Then call like

jul 2011 012
jul 2017 216
jul 2100 60

Answer 6

I realize this was asked ages ago, but none of the answers I see are what I consider pure BASH since they all use GNU date. I thought I would take a stab at answering... But I warn you ahead of time, the answer is not elegant, nor is it short at over 100 lines. It could be pared down, but I wanted to let others easily see what it does.

The primary "tricks" here are figuring out if a year is a leap year (or not) by getting the MODULUS % of the year divided by 4, and then just adding up the days in each month, plus an extra day for February if needed, using a simple table of values.

Please feel free to comment and offer suggestions on ways to do this better, since I'm primarily here to learn more myself, and I would consider myself a BASH novice at best. I did my best to make this as portable as I know how, and that means some compromises in my opinion.

On to the code... I hope it is pretty self-explanatory.

#!/bin/sh

# Given a julian day of the year and a year as ddd yyyy, return
# the values converted to yyyymmdd format using ONLY bash:

ddd=$1
yyyy=$2
if [ "$ddd" = "" ] || [ "$yyyy" = "" ]
then
  echo ""
  echo "   Usage: <command> 123 2016"
  echo ""
  echo " A valid julian day from 1 to 366 is required as the FIRST"
  echo " parameter after the command, and a valid 4-digit year from"
  echo " 1901 to 2099 is required as the SECOND. The command and each"
  echo " of the parameters must be separated from each other with a space."
  echo " Please try again."
  exit
fi
leap_yr=$(( yyyy % 4 ))
if [ $leap_yr -ne 0 ]
then
  leap_yr=0
else
  leap_yr=1
fi
last_doy=$(( leap_yr + 365 ))
while [ "$valid" != "TRUE" ]
do
  if [ 0 -lt "$ddd" ] && [ "$last_doy" -ge "$ddd" ]
  then
    valid="TRUE"
  else
    echo "   $ddd is an invalid julian day for the year given."
    echo "   Please try again with a number from 1 to $last_doy."
    exit    
  fi
done
valid=
while [ "$valid" != "TRUE" ]
do
  if [ 1901 -le "$yyyy" ] && [ 2099 -ge "$yyyy" ]
  then
    valid="TRUE"
  else
    echo "   $yyyy is an invalid year for this script."
    echo "   Please try again with a number from 1901 to 2099."
    exit    
  fi
done
if [ "$leap_yr" -eq 1 ]
then
  jan=31  feb=60  mar=91  apr=121 may=152 jun=182
  jul=213 aug=244 sep=274 oct=305 nov=335
else
  jan=31  feb=59  mar=90  apr=120 may=151 jun=181
  jul=212 aug=243 sep=273 oct=304 nov=334
fi
if [ "$ddd" -gt $nov ]
then
  mm="12"
  dd=$(( ddd - nov ))
elif [ "$ddd" -gt $oct ]
then
  mm="11"
  dd=$(( ddd - oct ))
elif [ "$ddd" -gt $sep ]
then
  mm="10"
  dd=$(( ddd - sep ))
elif [ "$ddd" -gt $aug ]
then
  mm="09"
  dd=$(( ddd - aug ))
elif [ "$ddd" -gt $jul ]
then
  mm="08"
  dd=$(( ddd - jul ))
elif [ "$ddd" -gt $jun ]
then
  mm="07"
  dd=$(( ddd - jun ))
elif [ "$ddd" -gt $may ]
then
  mm="06"
  dd=$(( ddd - may ))
elif [ "$ddd" -gt $apr ]
then
  mm="05"
  dd=$(( ddd - apr ))
elif [ "$ddd" -gt $mar ]
then
  mm="04"
  dd=$(( ddd - mar ))
elif [ "$ddd" -gt $feb ]
then
  mm="03"
  dd=$(( ddd - feb ))
elif [ "$ddd" -gt $jan ]
then
  mm="02"
  dd=$(( ddd - jan ))
else
  mm="01"
  dd="$ddd"
fi
if [ ${#dd} -eq 1 ]
then
  dd="0$dd"
fi
if [ ${#yyyy} -lt 4 ]
then
  until [ ${#yyyy} -eq 4 ]
  do
    yyyy="0$yyyy"
  done
fi
printf '\n   %s%s%s\n\n' "$yyyy" "$mm" "$dd"

Answer 7

OLD_JULIAN_VAR=$(date -u -d 1840-12-31 +%s)

TODAY_DATE=`date --date="$odate" +"%Y-%m-%d"`
TODAY_DATE_VAR=`date -u -d "$TODAY_DATE" +"%s"`
export JULIAN_DATE=$((((TODAY_DATE_VAR - OLD_JULIAN_VAR))/86400))
echo $JULIAN_DATE

mathematically represented below

[(date in sec)-(1840-12-31 in sec)]/(sec in a day 86400)

Answer 8

My solution in bash

from_year=2013
from_day=362

to_year=2014
to_day=5

now=`date +"%Y/%m/%d" -d "$from_year/01/01 + $from_day days - 2 day"`
end=`date +"%Y/%m/%d" -d "$to_year/01/01 + $to_day days - 1 day"`


while [ "$now" != "$end" ] ; 
do
    now=`date +"%Y/%m/%d" -d "$now + 1 day"`;
    echo "$now";
    calc_day=`date -d "$now" +%G'.'%j`
    echo $calc_day
done