A snippet which finds out whether a given date is DST (Daylight Saving Time) or not

dst.sh

#!/bin/bash

# Reference Source
# https://www.nist.gov/pml/time-and-frequency-division/popular-links/daylight-saving-time-dst
function is_dst()
{
	epoch_secs=$(date --date="$1" +%s)
	src_yr=$(date --date="$1" +%Y)

	mar1wday=$(date --date="$src_yr-03-01" +%w)
	nov1wday=$(date --date="$src_yr-11-01" +%w)

	# 2nd Sunday of March
	days=$((mar1wday % 7 + 7))
	dst_start=$(date --date="$src_yr-03-01 + $days days" +%s)

	# 1st Sunday of November
	days=$((nov1wday % 7))
	dst_stop=$(date --date="$src_yr-11-01 + $days days" +%s)

	if [[ $epoch_secs -gt $dst_start && $epoch_secs -le $dst_stop ]]; then
		return 1
	else
		return 0
	fi
}

for arg in $@; do
	is_dst $arg
	if [[ $? -eq 0 ]]; then
		echo no
	else
		echo yes
	fi
done