I plan to study VCV Rack. I want to keep track of changes by making regular timestamped backups.
To do this I wrote this simple 66-line script which watches the mtime of a file and makes a copy
whenever a change is detected.


```py
#!/usr/bin/env python3
import os
import time
import argparse
from datetime import datetime
import shutil



def now():
  a = datetime.now()
  return a.strftime("%Y_%m_%d_%H_%M_%S")

def when(fn):
  if os.path.exists(fn):
    return os.path.getmtime(fn)
  else:
    return -1

def loop(d):
  fns = list(d.keys())
  for fn in fns:
    cur = when(fn)
    if cur > d[fn]:
      d[fn] = cur
      make_copy(fn)
  
def make_copy(fn):
  n = now()
  if "." in fn:
    xs = fn.split(".")
    ext = xs.pop()
    basename = ".".join(xs)
    ofn = f"{basename}_{n}.{ext}"
  else:
    ofn = f"{fn}_{n}"
  ofn = f"{outdir}/{ofn}"
  shutil.copy(fn,ofn)
  print(f"{fn} => {ofn}") 

def main():
  global outdir
  parser = argparse.ArgumentParser(prog="autobak1",
                                  description="Automatically make timestamped copies of a watched file")
  parser.add_argument("-d","--output-dir",default=".",help="Where to put the auto backups")
  parser.add_argument("files",nargs="+")
  ns = parser.parse_args()
  outdir = ns.output_dir

  fns = ns.files
  d = {}
  for fn in fns:
    d[fn] = when(fn)

  try:
    while True:
      loop(d)
      time.sleep(1)
  except KeyboardInterrupt:
    print("C-c")
    return

if __name__ == "__main__":
  main()
```