Time ago in words within bash

time_ago.sh

#!/usr/bin/env bash
# Copyright (c) 2019 Ulysse Buonomo <buonomo.ulysse@gmail.com> (MIT license)
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

# Available at https://git.io/time_ago

time_ago() {
  if (( $# < 1 )); then
    local u=$(tput smul) # underline 
    local n=$(tput rmul) # no underline 
    echo "usage: time_ago ${u}timestamp_ago${n} [${u}timestamp_now${n}]"
    exit 1
  fi
  local minutes=60
  local hours=$(( 60 * minutes ))
  local days=$(( 24 * hours ))
  local diff=$(( ${2:-$(date +%s)} - $1 ))
  local human
  if (( diff < 30 )); then
    human="${diff} seconds"
  elif (( diff < 90 )); then
    human="1 minute"
  elif (( diff < 1 * hours )); then
    human="$(( (diff + minutes / 2) / minutes )) minutes"
  elif (( diff < 1 * hours + 30 * minutes )); then
    human="about 1 hour"
  elif (( diff < 1 * days )); then
    human="about $(( (diff + hours / 2) / hours )) hours"
  elif (( diff < 2 * days)); then
    human="1 day"
  else
    human="$(( (diff + days / 2) / days)) days"
  fi

  echo "$human ago"
}

if [[ "$0" = "./time_ago" ]];then
  time_ago 1556324045 1556540404 # 3 days ago 
  time_ago 1556424045 1556540404 # 1 day ago 
  time_ago 1556534045 1556540404 # about 2 hours ago
  time_ago 1556536045 1556540404 # about 1 hour ago
  time_ago 1556539145 1556539875 # 12 minutes ago 
  time_ago 1556539900 1556539921 # 21 seconds ago
  time_ago # shows usage and exit with status 1
fi