fix(user/bk-copy-rand-music):Follow direct symlinks to files

[BK-2020-03.git] / unitproc / bkt-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 0.2.3
    # Input: arg1: 'date'-parsable timestamp string (optional)
    # Output: Nanoseconds since 1970-01-01
    # Depends: date 8, cut 8, yell()
    # Ref/Attrib: Force base 10 Bash arith with '10#'. https://stackoverflow.com/a/24777667
    local argTime timeCurrent timeInput timeEpochFloat timeEpochInt
    local timeEpochNsFrac timeEpochNs

    argTime="$1";

    # Get Current Time
    timeCurrent="$(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 "$argTime" ]]; then
	## T: Time argument empty, use current time
	timeInput="$timeCurrent";
    else
	## F: Time argument exists, validate time
	if date --date="$argTime" 1>/dev/null 2>&1; then
	    ### T: Time argument is valid; use it
	    timeInput="$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    
    timeEpochFloat="$(date --date="$timeInput" +%s.%N)"; # Save ssss.NNNNNNNNN
    timeEpochInt="$(echo "$timeEpochFloat" | cut -d. -f1)"; # Get ssss
    timeEpochNsFrac="$(echo "$timeEpochFloat" | cut -d. -f2)"; # Get NNNNNNNNN
    timeEpochNs="$(( (10#"$timeEpochInt" * 10**9) + (10#"$timeEpochNsFrac") ))";
    echo "$timeEpochNs";
} # 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+