Watch following/followers and generates diff. (crontab required)

followlog.sh

#!/bin/zsh
# (only tested with zsh, anyway)
#
# followlog.sh
#
# (c) 2016 Kuriyama hibiya
#     All rights reserved.
#
# Usage:
#
#  1. Place this script with a directory named as account name to track.
#  2. Attach this to crontab like this: (ACCOUNT_TO_READ should be logged in .trc)
#    */4 * * * * /home/hibiya/followlog/crontab.sh <READER_ACCOUNT> 2> /dev/null
#  3. Wait for mail from cron.
#
# Warning:
#
#  * target account SHOULD visible by READER_ACCOUNT.
#   logging is unavailable when:
#    * target account blocked READER_ACCOUNT
#    * target account is protected, but READER_ACCOUNT doesn't follow target
#    * etc
#  * Twitter's API limited to 15 request / 15 minutes, so you cannot set
#   cron rule's divider (*/n) more than count of accounts.
#
# Shell/Env Requirements:
#
#  * `dir/*(.)`
#  * GNU sed
#
# Requirements:
#  https://github.com/sferik/t
#

cd "$(dirname "$0")"

d=$(date +%Y/%m)
file=$(date +%d-%H-%M)

t set account $1 > /dev/null

function load {
  # $1: 'followers', 'followings'
  # $2: account name
  # $3: retval

  local dir=$2/$1/$d
  local csv=$(t $1 --csv $2 2> /dev/null)
  local header="[$1/@$2]"

  # limited
  if [ "$?" -ne "0" ]; then
    >&2 echo "$header\tRate Limited!"
    exit 1
  fi

  if [ ${#csv} -lt 2 ]; then
    >&2 echo "$header\tGot empty list!"
    exit 1
  fi

  list=$(echo $csv | grep -E '^[0-9]+,(.+,){8,}' | cut -d, -f1,9 | sort)

  # first logging of month
  if [ ! -d "$dir/diff" ]; then
    >&2 echo "[$1/@$2]\tWriting first log."
    mkdir -p $dir/diff 2> /dev/null
    echo $list > $dir/$file

  else
    local lastlog=$(echo $dir/*(.) | tr ' ' '\n' | sort | tail -n 1)
    local differ=$(echo $list | diff -a -u $lastlog - | grep -E "^[+-][^+-]")
    local lines=$(echo "$differ" | wc -l)

    echo "$differ" | grep -q "Binary file (standard input) matches"
    if [ $? -eq 0 ]; then
      >&2 echo "$header\tgrep treated stdin as binary!"
      exit 1
    fi

    # something changed
    if [ -n "$differ" ]; then
      if [ ! -f "$2/.no-mail" ]; then
        echo $differ | sed -e "s/^/[$1\/@$2]\t/"
        echo
      fi

      >&2 echo "$header\tdiffer!"

      echo $list > $dir/$file
      echo $differ > $dir/diff/$file

    else
      eval $1=''
      >&2 echo "$header\tNothing changed."
    fi
  fi
}

for i in $(ls -d */); do
  account=${i%%/}

  load followings $account &
  pid1=$!
  load followers $account &
  pid2=$!

  wait $pid1
  wait $pid2

done