Bash script that calculates age of each folder in a directory, based on git commits

project-age.sh

#!/usr/bin/env bash

# http://www.daveeddy.com/2014/06/29/human-readable-duration-in-bash/
human() {
    local seconds=$1
    if ((seconds < 0)); then
        ((seconds *= -1))
    fi

    local times=(
    $((seconds / 60 / 60 / 24 / 365)) # years
    $((seconds / 60 / 60 / 24 / 30))  # months
    $((seconds / 60 / 60 / 24 / 7))   # weeks
    $((seconds / 60 / 60 / 24))       # days
    $((seconds / 60 / 60))            # hours
    $((seconds / 60))                 # minutes
    $((seconds))                      # seconds
    )
    local names=(year month week day hour minute second)

    local i
    for ((i = 0; i < ${#names[@]}; i++)); do
        if ((${times[$i]} > 1)); then
            echo "${times[$i]} ${names[$i]}s"
            return
        elif ((${times[$i]} == 1)); then
            echo "${times[$i]} ${names[$i]}"
            return
        fi
    done
    echo '0 seconds'
}

directory_age() {
  local f=$1
  echo -n "${f}: "

  newest=`git rev-list --parents HEAD --format=%at -- ${f} | (head -n2 | tail -n1)`
  oldest=`git rev-list --parents HEAD --format=%at -- ${f} | tail -n1`
  if [ -z ${newest} ]
    then
    echo "skipped (failed to parse commits)"
    continue
  fi

  difference=`expr ${newest} - ${oldest}`
  human ${difference}
}

echo "Project Ages:"
echo "================"
for f in *; do
  [ -d "${f}" ] || continue
  [ ${f} = "archive" ] && continue
  directory_age ${f}
done