style(unitproc):appendFileTar():VAR_NAME to varName

[BK-2020-03.git] / unitproc / bktemp-timeEpochNS

#!/bin/bash
# Desc: Get timestamp in nanoseconds

yell() { echo "$0: $*" >&2; }      #o Yell, Die, Try Three-Fingered Claw technique
die() { yell "$*"; exit 111; }     #o Ref/Attrib: https://stackoverflow.com/a/25515370
try() { "$@" || die "cannot $*"; } #o
timeEpochNS() {
    # Desc: Get epoch nanoseconds
    # Usage: timeEpochNS
    # Version 0.2.2
    # Input: arg1: 'date'-parsable timestamp string (optional)
    # Output: Nanoseconds since 1970-01-01
    # Depends: date 8, yell()
    # Ref/Attrib: Force base 10 Bash arith with '10#'. https://stackoverflow.com/a/24777667
    local TIME_CURRENT TIME_INPUT TIME_EPOCH_FLOAT TIME_EPOCH_NSFRAC
    local TIME_EPOCH_NS

    argTime="$1";

    # Get Current Time
    TIME_CURRENT="$(date --iso-8601=ns)"; # Produce `date`-parsable current timestamp with resolution of 1 nanosecond.

    # Decide to parse current or supplied time
    ## Check if time argument empty
    if [[ -z "$argTime" ]]; then
	## T: Time argument empty, use current time
	TIME_INPUT="$TIME_CURRENT";
    else
	## F: Time argument exists, validate time
	if date --date="$argTime" 1>/dev/null 2>&1; then
	    ### T: Time argument is valid; use it
	    TIME_INPUT="$argTime";
	else
	    ### F: Time argument not valid; exit
	    yell "ERROR:Invalid time argument supplied. Exiting."; exit 1;
	fi;
    fi;
    # Construct and deliver nanoseconds since 1970-01-01    
    TIME_EPOCH_FLOAT="$(date --date="$TIME_INPUT" +%s.%N)"; # Save ssss.NNNNNNNNN
    TIME_EPOCH_INT="$(echo "$TIME_EPOCH_FLOAT" | cut -d. -f1)"; # Get ssss
    TIME_EPOCH_NSFRAC="$(echo "$TIME_EPOCH_FLOAT" | cut -d. -f2)"; # Get NNNNNNNNN
    TIME_EPOCH_NS="$(( (10#"$TIME_EPOCH_INT" * 10**9) + (10#"$TIME_EPOCH_NSFRAC") ))";
    echo "$TIME_EPOCH_NS";
} # Nanoseconds since 1970-01-01

#==BEGIN sample code==
echo "It's been $(timeEpochNS) nanoseconds since 1970-01-01.";
echo "It's been $(timeEpochNS "10 years ago") nanoseconds since 10 years ago.";
echo "It's been $(timeEpochNS "2003-02-01T08:59:15-05:00") nanoseconds since contact lost with STS-107.";
#==END sample code==

# Author: Steven Baltakatei Sandoval
# License: GPLv3+