Mac OS X BSD date, convert UTC time to local time

Take a given UTC time and convert to a local time string in CCYYMMDDhhmm.SS format.
Offset the given time by minus 20 seconds (the -20S argument to -v).

date \
	-jf "%Y-%m-%dT%H:%M:%S %z" \
	-v -20S \
	"2016-04-11T03:26:02 +0000" \
	"+%Y%m%d%H%M.%S"

This output can then be pumped into something like touch:

dateTouch=$(
	date \
		-jf "%Y-%m-%dT%H:%M:%S %z" \
		-v -20S \
		"2016-04-11T03:26:02 +0000" \
		"+%Y%m%d%H%M.%S"
)

touch -t "$dateTouch" /path/to/my/file

Or as a Linux/OSX compatible Bash function for:

Taking a UTC date in YYYY-MM-DDTHH:MM:SS format and a positive/negative seconds offset.
Return a CCYYMMDDhhmm.SS format date in local time.

function getUTCDateSecondOffset {

	# Linux or BSD date?
	set +e
	date -v 0S >/dev/null 2>&1
	retVal=$?
	set -e

	if [[ $retVal -eq 0 ]]; then
		# BSD date
		date \
			-jf "%Y-%m-%dT%H:%M:%S %z" \
			-v "${2}S" \
			"${1} +0000" \
			"+%Y%m%d%H%M.%S"

	else
		# Linux date
		date --date "${1} +0000 ${2} seconds" "+%Y%m%d%H%M.%S"
	fi
}

getUTCDateSecondOffset "2016-04-11T03:26:02" "-20"
# 201604111325.42

magnetikonline/README.md

Mac OS X BSD date, convert UTC time to local time

Reference