scripts/file_utils/unln.py

#!/usr/bin/python3
#
# unln.py, Copyright © 2013 Matteo Cypriani <mcy@lm7.fr>
#
########################################################################
# This program is licensed under the terms of the Expat license.
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
# CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
########################################################################
#
# This script separates file names given as arguments from their respective
# inodes by doing the equivalent of (cp -p file tmp && mv tmp file).
#
# TODO:
# - Handle exceptions (permission denied on copy, etc.)
# - Option verbose
# - Option to follow symlinks
# - Summarise skipped regular files with more than one link


import sys
import os
import tempfile
import shutil


def verbose(*message, **args):
    """Prints the message on the standard output if verbose mode is on.

    This function is a simple wrapper around print(), and you can use any
    keyword argument you would use with print().
    """
    if options["verbose"]:
        print(*message, **args)

def warn(*message, prefix="Warning:", **args):
    """Prints the message on the error output, prepended by 'prefix'.

    This function is a simple wrapper around print(), and you can use any
    keyword argument you would use with print().
    """
    print(prefix, *message, file=sys.stderr, **args)

def error(error_code, *message, **args):
    """Prints the message on the error output and exits.

    This function is a simple wrapper around print(), and you can use any
    keyword argument you would use with print().
    """
    print(*message, file=sys.stderr, **args)
    sys.exit(error_code)

def quote(string):
    """ Quotes a string. """
    return "``{}´´".format(string)


# Default options
options = {
    "verbose": True
    }

# Name of this program
progname = os.path.basename(sys.argv[0])

# Short usage string
usage_string = "Usage:\n\t{} <file1> [file2 ...]\n".format(progname)

# Error codes
ERR_BAD_USAGE = 1


# Check command-line arguments
if len(sys.argv) < 2:
    error(ERR_BAD_USAGE, usage_string)


# Main loop
for filename in sys.argv[1:]:
    # Exists?
    if not os.path.exists(filename):
        warn(quote(filename), "does not exist, ignoring.")
        continue

    # Is a symbolic link?
    if os.path.islink(filename):
        warn(quote(filename), "is a symbolic link, ignoring.")
        continue

    # Is a regular file?
    if not os.path.isfile(filename):
        warn(quote(filename), "is not a regular file, ignoring.")
        continue

    # Number of links?
    nlinks = os.stat(filename).st_nlink
    if nlinks == 1:
        verbose(quote(filename), "has only one link, ignoring.")
        continue

    verbose(quote(filename), "has", nlinks, "hard links, proceeding", end="... ")

    # Reserve a temporary file name
    dirname = os.path.dirname(filename)
    handle, tmpfilename = tempfile.mkstemp(
        prefix="{}-".format(filename),
        suffix="-{}.tmp".format(progname),
        dir=dirname)
    os.close(handle) # we just need a temporary file name

    # Copy the original file to the temporary file
    verbose("Copying to temporary file", quote(tmpfilename), end="... ")
    shutil.copy2(filename, tmpfilename) # cp -p

    # Try to sync if we are running Python >= 3.3
    if sys.version_info.minor >= 3:
        verbose("Syncing", end="... ")
        os.sync()

    # Rename the temporary file with the original file name
    verbose("Moving back {} to {}...".format(
            quote(tmpfilename), quote(filename)))
    os.rename(tmpfilename, filename)