unitproc/bkdstcountdown

   1 #!/usr/bin/env bash
   2 # Description: Outputs days until next timezone discontinuity
   3 # Depends: GNU Coreutils 8.32 (date), zdump 2.35, Bash 5.1.16
   4 #   BK-2020-03: yell(), die(), must()
   5 # Version: 0.1.0
   6
   7 # User config
   8 script_tz="America/Los_Angeles"; # Timezone to check for discontinuities
   9
  10 yell() { echo "$0: $*" >&2; } # Yell, Die, Try Three-Fingered Claw technique; # Ref/Attrib: https://stackoverflow.com/a/25515370
  11 die() { yell "$*"; exit 111; }
  12 must() { "$@" || die "cannot $*"; }
  13 main() {
  14     declare -a datesDiscontArray; #array
  15
  16     # plumbing
  17     script_year="$(date +%Y)";
  18     script_year_next="$(( script_year + 1 ))";
  19     script_year_next2="$(( script_year + 2 ))";
  20     script_run_date_seconds="$(date +%s)";
  21
  22     # Get discontinuity dates from zdump (see https://stackoverflow.com/a/613580 )
  23     datesDiscont="$(zdump -c "$script_year","$script_year_next2" -v $script_tz | \
  24       grep "$script_year\|$script_year_next" | \
  25       awk '{ print $2 " " $3 " " $4 " " $5 " " $6 " " $7 }'; echo)"; # get dates
  26     if [[ -z "$datesDiscont" ]]; then
  27         yell "STATUS:No time discontinuity this year.";
  28         exit 1;
  29     fi;
  30
  31     # Convert datesDiscont into array
  32     while read -r line; do
  33         tunix="$(date --date="$line" +%s)"; # get unix epoch seconds
  34         datesDiscontArray+=("$tunix");
  35     done < <(printf "%s\n" "$datesDiscont");
  36
  37     # Sort datesDiscontArray
  38     while read -r line; do
  39         datesDiscontArray+=("$line");
  40     done < <(printf "%s\n" "${datesDiscontArray[@]}" | sort);
  41
  42     # # Get earliest date in datesDiscontArray that isn't in the past.
  43     for discontinuityDate in "${datesDiscontArray[@]}"; do
  44         if [[ $discontinuityDate -gt $script_run_date_seconds ]]; then
  45             nextDiscontDate="$discontinuityDate";
  46             break;
  47         fi;
  48     done;
  49
  50     # Check that nextDiscontDate is not empty
  51     if [[ -z "$nextDiscontDate" ]]; then
  52         die "FATAL:nextDiscontDate empty";
  53     fi;
  54
  55     # Calculate days until next discontinuity date
  56     output="$(( ( nextDiscontDate - script_run_date_seconds )/86400 )) days";
  57     printf "%s\n" "$output";
  58
  59 }; # main program
  60
  61 main "$@";
  62
  63 # Author: Steven Baltakatei Sandoval
  64 # License: GPLv3+