watch.py

# Usage: watch.py [pattern] [command...]
#
# Watches files for changes and calls a command when a new file has been created
# or an existing file has been modified.  A single % in the command will be
# replaced by the path of the created/modified file.
#
# Examples:
#   watch.py *.tex pdflatex main.tex
#   watch.py *.dot dot -Tpdf -O %

import glob
import os
import subprocess
import sys
import time

CHANGE_CREATED = 0
CHANGE_DELETED = 1
CHANGE_MODIFIED = 2

def create_snapshot(pattern):
  return {path: os.stat(path).st_mtime for path in glob.iglob(pattern)}

def compare_snapshots(prev, now):
  changes = []
  for path in now:
    if path not in prev:
      changes.append((CHANGE_CREATED, path))
    elif prev[path] < now[path]:
      changes.append((CHANGE_MODIFIED, path))
  for path in prev:
    if path not in now:
      changes.append((CHANGE_DELETED, path))
  return changes

pattern = sys.argv[1]
command = sys.argv[2:]

prev = create_snapshot(pattern)

while True:
  time.sleep(1)

  now = create_snapshot(pattern)

  for change, path in compare_snapshots(prev, now):
    if change == CHANGE_DELETED:
      print('[DEL] ' + path)
    elif change == CHANGE_CREATED:
      print('[CRE] ' + path)
    elif change == CHANGE_MODIFIED:
      print('[MOD] ' + path)

    if change == CHANGE_CREATED or change == CHANGE_MODIFIED:
      c = [path if arg == '%' else arg for arg in command]
      subprocess.call(c)

  prev = now