Small tool to do poor-man's logrotate and update a "latest" symlink

clean-all-but.py

#! /usr/bin/env python2
# Copyright (C) 2016 Sebastian Pipping <[email protected]>
# Licensed under AGPL v3 or later

from __future__ import print_function

import argparse
import errno
import os
import re
import sys
import stat


def _try_int(text):
    try:
        return int(text)
    except ValueError:
        return text


def natural(key):
    return [_try_int(m.group(0)) for m in re.finditer('[0-9]+|[^0-9]+', key)]


def good_ones(sorted_files, symlink):
    for i, filename in enumerate(sorted_files):
        if filename == symlink:
            continue

        try:
            st = os.lstat(filename)
        except OSError:
            continue
        else:
            if stat.S_ISLNK(st.st_mode):
                continue

            if st.st_size == 0 and i != len(sorted_files) - 1:
                continue

        yield filename


def clean_all_but(keep_count, sorted_files, verbose):
    assert keep_count >= 0
    keeping = sorted_files[-keep_count:]
    if verbose:
        for filename in keeping:
            print('Kept "%s".' % filename)

    deleting = sorted_files[:-keep_count]
    for filename in deleting:
        if verbose:
            print('Removing "%s"...' % filename)
        os.remove(filename)

    return (keeping, deleting)


def rewrite_symlink(filename, content, verbose):
    if verbose:
        print('Making "%s" point to "%s"...' % (filename, content))

    try:
        st = os.lstat(filename)
    except OSError as e:
        if e.errno != errno.ENOENT:
            raise
    else:
        if not stat.S_ISLNK(st.st_mode):
            raise OSError(errno.ENOLINK, 'Not a link: "%s"' % filename)
        os.remove(filename)

    os.symlink(content, filename)


def main(options):
    if not options.files:
        return

    try:
        if not stat.S_ISLNK(os.lstat(options.symlink).st_mode):
            return
    except OSError as e:
        if e.errno != errno.ENOENT:
            raise

    (kept, _) = clean_all_but(
            options.keep_count,
            list(good_ones(sorted(options.files, key=natural), options.symlink)),
            options.verbose)

    if kept:
        rewrite_symlink(options.symlink, kept[-1], options.verbose)


if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('--verbose', '-v', default=False, action='store_true')
    parser.add_argument('keep_count', type=int, metavar='COUNT',
            help='number of files to keep')
    parser.add_argument('symlink', metavar='SYMLINK',
            help='path of symlink to re-wire')
    parser.add_argument('files', nargs='*', metavar='FILE',
            help='file to remove potentially')

    options = parser.parse_args()
    sys.exit(main(options))