bash - calculate balance on certain day from monthly projection -

i have list of monthly outgoings looks this:

1st - car - 100

3rd - rent - 400

7th - gas , electricity - 51

8th - phone - 12

17th - internet - 30.74

21st - insurance - 45.21

27th - patreon - 2

28th - water - 12.9

the above example similar in structure monthly outgoings.

let's paid on 23rd of every month. write script (preferably in bash) input current bank balance , subtract that's coming out of bank between $current_date , 22nd of month?

so run script time in month , quick glance @ how surplus money have.

here's annotated bash solution, not optimal solution:

#! /bin/bash  if [[ -z ${1} ]];     echo "missing argument: current balance"     exit 2 fi  # current balance comes in first argument, multiplied 100 cent-value (bc decimal) current_balance=$(scale=0; echo "${1} * 100" | bc -l) # current day without leading 0 current_day=$(date +"%-d") # last day of current month last_day_of_month=$(date -d "-$(date +%d) days +1 month" +"%d") # default target date 22. target_day=22 offset=0  # if we're past cut-off point, we'll check until 22. of next month if (( ${current_day} > 22 ));     target_day=$(( ${last_day_of_month} + 22 ))     offset=$(( $last_day_of_month )) fi  # set outgoings on index of date cent-values outgoings=() outgoings[1]=10000 outgoings[3]=40000 outgoings[7]=5100 outgoings[8]=1200 outgoings[17]=3074 outgoings[21]=4521 outgoings[27]=200 outgoings[28]=1290  # iterate on days until hit target (( i=${current_day}; < ${target_day}; += 1 ));     # decrement offset (either 0 or amount of days in month)     if (( $i > ${offset} ));          index=$(( $i - $offset ))     else         index=$(( $i ))     fi     # if no outgoings day, continue     if [[ -z "${outgoings[index]}" ]]; continue; fi     # calculate current balance after days outgoings     current_balance=$(( $current_balance - ${outgoings[index]} )) done  # divide current left on balance 100 euro/dollar/whatever amount left_over=$(echo "scale=2; ${current_balance} / 100" | bc -l)  echo "extra money: ${left_over}"