stopwatch.sh

#!/usr/bin/env bash

# Measure time
# Usage: stopwatch [start|stop|print]
function stopwatch {
  case "$1" in
    start)
      # start new stopwatch
      STOPWATCH+=($(date -u +%s))
      ;;
    stop)
      # stop last started stopwatch
      if [[ ${#STOPWATCH[@]} > 0 ]]; then
        unset STOPWATCH[$((${#STOPWATCH[@]}-1))]
      fi
      ;;
    print)
      # print last started (but not stopped) stopwatch's elapsed time
      if [[ ! -z $STOPWATCH ]]; then
        local start=${STOPWATCH[$((${#STOPWATCH[@]}-1))]}
        local now=$(date -u +%s)
        local elapsed=$((now-start))
        local hours=$((elapsed/3600))
        local minutes=$((elapsed%3600/60))
        local seconds=$((elapsed%60))
        printf '%.0f:%2.0f:%2.0f' $hours $minutes $seconds | tr ' ' '0'
      fi
      ;;
  esac
}

# Example usage:

function taskA {
  echo "Task A started"
  stopwatch start
  sleep 2
  echo "Task A finished in $(stopwatch print)"
  stopwatch stop
}

function taskB {
  echo "Task B started"
  stopwatch start
  local i
  for ((i=1; i<=3; i++)); do
    sleep 1
    if [[ $i == 2 ]]; then
      taskC
    fi
  done
  echo "Task B finished in $(stopwatch print)"
  stopwatch stop
}

function taskC {
  echo "Task C started"
  stopwatch start
  local i
  for ((i=1; i<=3; i++)); do
    sleep 1
  done
  echo "Task C finished in $(stopwatch print)"
  stopwatch stop
}

stopwatch start
taskA
sleep 1
taskB
echo "Total time: $(stopwatch print)"

# Output:
# Task A started
# Task A finished in 0:00:02
# Task B started
# Task C started
# Task C finished in 0:00:03
# Task B finished in 0:00:06
# Total time: 0:00:09