CODEWITHSUNDEEP
bashshell
Deepika Jantz
Deepika Jantz

Reputation: 49

How to get second sunday in a Month given a date parameter in bash script

I am trying to write a bash script, to merge 24 files in a given day. The requirement changes during Day light saving time changes, where I get 23 or 25 files.

So, with further research I realized that day-light savings begins on the second Sunday of March(23) of every year and ends on first sunday of Novemeber(25).

I need more inputs to get second sunday in a given month to do the check of finding 23 or 25 files for March and November respectively.

Any inputs to help me with this will be really appreciated.

Thank you

Here is the sample code to find 24 files in a day-

if [ -z "$1" ];then
now=$(date -d "-1 days" +%Y-%m-%d);
else now=$1;
fi
load_date='load_date='$now
singlePath="$newPath/$load_date"
fileCount=$(hdfs dfs -ls -R  $hdfsPath/$load_date/ | grep -E '^-' | wc -l)
path=$hdfsPath/$load_date
if [ $fileCount -eq 24 ]; then
echo "All files are available for "$load_date;
hadoop fs -cat $path/* | hadoop fs -put - $singlePath/messages.txt
else echo $fileCount" files are available for "$load_date"! Please note, few files are being missed";
fi

Upvotes: 1

Views: 820

Answers (1)

glenn jackman
glenn jackman

Reputation: 246799

I wouldn't hardcode the dates of DST transistions. I would just count "how many hours did today have":

  1. a "normal" day:

    $ diff=$(( $(date -d now +%s) - $(date -d yesterday +%s) ))
$ echo $(( diff / 3600 ))
24

  2. "spring forward"

    $ diff=$(( $(date -d "2019-03-10 23:59:59" +%s) - $(date -d "2019-03-09 23:59:59" +%s) ))
$ echo $(( diff / 3600 ))
23

  3. "fall back"

    $ diff=$(( $(date -d "2019-11-03 23:59:59" +%s) - $(date -d "2019-11-02 23:59:59" +%s) ))
$ echo $(( diff / 3600 ))
25

One thing to note: since bash only does integer arithmetic, if the difference is not 86400 but 86399, you get: 

$ echo $((86399 / 3600))
23

So, better to query yesterday's time first in the tiny-but-non-zero chance that the seconds tick over between the 2 date calls:

diff=$(( -$(date -d yesterday +%s) + $(date -d now +%s) ))

Here, $diff will be 86400 or 86401 (for non DST transition days), and dividing by 3600 will give 24 not 23.

Upvotes: 3

Related Questions