difftree-touch

#! /usr/bin/env python3

# Reads an output logfile produced by difftree and touches each file
# mentioned in it, that is, sets access and modification times to the
# current time.  This seems to trigger Time Machine to "notice" that
# the files need to be backed up.  (For good measure, for each file
# touched, the parent directory is also touched.)  Thus, if there are
# persistent differences between a filesystem and its Time Machine
# backups, running this script causes those differences to be
# eliminated in the next backup.
#
# Usage: difftree-touch label=tree logfile
#
# `tree` should be the (non-backup) directory tree difftree was
# originally run against.  For example, if difftree was run against
# the home directory with label "current", then this script would be
# invoked as:
#
# difftree-touch current=$HOME logfile
#
# Greg Janee <gregjanee@gmail.com>

import errno
import os
import re
import sys

def format_exception(exception):
    return f"{type(exception).__name__}: {exception!s}"

def error(exception_type, exception, traceback):
    print("difftree-touch: " + format_exception(exception), file=sys.stderr)
    sys.exit(1)
sys.excepthook = error

if len(sys.argv) != 3 or not re.match("(\w+)=(.*)", sys.argv[1]):
    print("Usage: difftree-touch label=tree logfile", file=sys.stderr)
    sys.exit(1)

label, tree = re.match("(\w+)=(.*)", sys.argv[1]).groups()
logfile = sys.argv[2]

def touch(file):
    try:
        os.utime(file, follow_symlinks=False)
    except OSError as e:
        if e.errno == errno.ENOENT:
            print(
                f"difftree-touch: warning: {format_exception(e)}: {file}",
                file=sys.stderr
            )
        else:
            raise

for line in open(logfile):
    m = (
        re.match("(file|directory) (.*) differs$", line[:-1])
        or re.match(f"only in {label}: (file|directory) (.*)", line[:-1])
    )
    if m:
        file = os.path.join(tree, m.group(2))
        touch(file)
        touch(os.path.dirname(file))