BASH: A truly awful way to guarantee timestamp alignment across OS's...

timestamp-helper.sh

#!/usr/bin/env bash
# timestamp-helper.sh
# ------------------------------------------------------------------------------
# Command perfs observed on localhost.
#   date   : ~0.001-0.002s
#   gdate  : unknown
#   python   : ~0.015-0.030s
#   c    : ~0.025-0.049s
#   this.sh  : ~0.005-0.015s (with date, so + ~0.004-0.013s)
#
# ------------------------------------------------------------------------------
# Defaults
# ------------------------------------------------------------------------------
arg_g_val='ns'
arg_z_val="Z"
arg_t_val=9
# ------------------------------------------------------------------------------
# Help & Args
# ------------------------------------------------------------------------------
show_help() {
cat << EOF

This is a timestamp helper script, ensuring alingment of timestamps across OS's.
NOTE: This script is mostly for addressing the limitations of MacOS's 'date' command,
    but it will work anywhere 'cc' is available, and 'date' supports the '-u'
    and '-d' arguments.

Use: ${0##*/} -e {-r}
  -g   GRANULARITY      The environment in which to deploy.
                            Options: date, h|hour(s), m|minute(s), s|second(s), ns (default)
  -z   TZFORMAT         The format for TZ/UTC indicator.
                            Options: 'Z', '0' (zero)
  -t   TRIM             Trim the ns field to 'n' lenth. Default is '9'.
                            Options: 3, 6
  -p   PRESERVE         OSX: Preserves the c program 'cts' for your user elsewhere. This
                        file can be renamed.
                            Usage: ./cts
  -d   DEMO             Demo this helper.
                            TIP: 'watch -n0.01 ./timestamp-helper.sh -d'
  -h   HELP             Show this menu.

Examples:
  Timestamp with nanosecond granularity:
    ./${0##*/}
  Timestamp with hour granularity:
    ./${0##*/} -g hour
  Timestamp with ns granularity to the 3rd place and +00:00 as the TZ indicator.
    ./${0##*/} -t 3 -z 0

EOF
exit 1
}

OPTIND=1
while getopts "hg:z:t:dp" opt; do
  case "$opt" in
  h)
    show_help
    ;;
  g)
    arg_g='set'
    arg_g_val="$OPTARG"
    ;;
  d)
    arg_d='set'
    ;;
  t)
    arg_t_val="$OPTARG"
    ;;
  z)
    arg_z_val="$OPTARG"
    ;;
  p)
    arg_p='set'
    ;;
  :)
    echo "ERROR: Option -$OPTARG requires an argument."
    show_help
    ;;
  *)
    echo "ERROR: Unknown option!"
    show_help
    ;;
  esac
done
shift "$((OPTIND-1))"

case $arg_t_val in
  3)
    n=3
    ;;
  6)
    n=6
    ;;
  9)
    n=9
    ;;
  *)
    echo "ERROR: Unknown TRIM length."
    show_help
  ;;
esac

case $arg_z_val in
  Z)
    z="Z"
    ;;
  0)
    z="+00:00"
    ;;
  *)
    echo "ERROR: Unknown TZ format option."
    show_help
  ;;
esac

# ------------------------------------------------------------------------------
# Main Operations
# ------------------------------------------------------------------------------

# Detect OS
case "$OSTYPE" in
  solaris*) export OS_TYPE="SOLARIS" ;;
  darwin*)  export OS_TYPE="OSX" ;;
  linux*)   export OS_TYPE="LINUX" ;;
  bsd*)   export OS_TYPE="BSD" ;;
  msys*)  export OS_TYPE="WINDOWS" ;;
  cygwin*)  export OS_TYPE="CYGWIN" ;;
  *)    export OS_TYPE="unknown: $OSTYPE" ;;
esac

# Linux is easy.
[[ $OS_TYPE == "LINUX" ]] && tsCmd="date -u +%s%${n}N"
# MacOS takes a bit of effort...
#   The 'date' command doesn't support %N or --iso-8601='ns'
if [[ $OS_TYPE == "OSX" ]]; then
  # Try to get nanoseconds with gdate if it's installed.
  if command -v gdate &> /dev/null; then
    tsCmd="gdate --utc +%FT%T.%${n}NZ"
  elif command -v python &>/dev/null; then
  # Try to get nanoseconds with time_ns
  # REF: https://docs.python.org/3/library/time.html#time.clock_gettime_ns
    for v in 3.{7..20}; do
      if command -v python${v} &>/dev/null; then
      tsCmd="python${v} -c 'import time; import math; ns = int(str(time.time_ns())[:16]); print(ns)'"
      break
      fi
    done
  else
  # Finally force the matter by building a c program to print %s%N...
    if [[ ! -f cts ]]; then
      cat << EOF > epochInµsec.c
#include <stdio.h>
#include <sys/time.h>

int main(void)
{
  struct timeval time_now;
  gettimeofday(&time_now,NULL);
  int s = time_now.tv_sec;
  int us = time_now.tv_usec;
  printf("%10d%0${n}d\n",s,us);
  return 0;
}
EOF
      cc -o cts epochInµsec.c
      rm -f epochInµsec.c
    fi
    tsCmd='./cts'
  fi
fi

ts=$($tsCmd)
s=${ts:0:10}
ns=${ts:10}

function ts_demo() {
  printf "%s\n" "This helper ensures timestamp format alignment across" \
                "Unix, Linux, MacOS, and maybe BSD operating systems." \
                "" \
                "s:        $s" \
                "ns:                 $ns" \
                "s & ns:   $ts" \
                "" \
                "Examples:" \
                "    ./${0##*/} -g seconds" \
                "        $(echo $(./${0##*/} -g seconds))" \
                "    ./${0##*/} -g ns -t 3 -z 0" \
                "        $(echo $(./${0##*/} -g ns -t 3 -z 0))" \
                "    ./${0##*/}" \
                "        $(echo $(./${0##*/}))"
}

function cleanup() {
  if [[ ! -n ${arg_p+x} ]]; then
    rm -f cts
  fi
}

if [[ -n ${arg_d+x} ]]; then
  ts_demo
  cleanup
  exit
else
  case "$arg_g_val" in
    d|date)
      printf "%s\n" "$(date -ud @$s +"%F${z}")"
      ;;
    h|hour|hours)
      printf "%s\n" "$(date -ud @$s +"%FT%H${z}")"
      ;;
    m|minute|minutes)
      printf "%s\n" "$(date -ud @$s +"%FT%H:%M${z}")"
      ;;
    s|second|seconds)
      printf "%s\n" "$(date -ud @$s +"%FT%H:%M:%S${z}")"
      ;;
    ns|:)
      printf "%s\n" "$(date -ud @$s +"%FT%H:%M:%S,${ns}${z}")"
      ;;
    *)
      echo "ERROR: Unknown option!"
      show_help
      ;;
  esac
fi

cleanup

Gawd it's awful...
Could remove the OS detection and sub in for simply checking if 'date -u +'%s%N' outputs 19 characters, then fallback to other mechanisms.