Script for changing all absolute links in a given directory to symlinks, UNIX only

abs2rel.py

#!/usr/bin/env python

"""
Script for changing all absolute links in a given directory to symlinks, UNIX only.


Requirements:
    * Python >= 2.7.x or Python 3.x

Author:
    Wibowo Arindrarto <bow@bow.web.id>

No Rights Reserved. This script is in the public domain.
"""
from __future__ import print_function

import argparse
import os
from os import path


def is_abs_link(fname):
    return path.islink(fname) and path.isabs(os.readlink(fname)) and path.exists(fname)


def calc_relative(frm, to):
    # outputs relative path from frm to to
    # both inputs must be absolute paths
    common = path.commonprefix([path.dirname(frm), path.dirname(to)]) + path.sep
    if not common.endswith(path.sep):
        common += path.sep
    to_uniq = to.replace(common, "")
    frm_uniq = frm.replace(common, "")

    dist = max(0, len(frm_uniq.split(path.sep)) - 1)

    if dist > 0:
        return (".." + path.sep) * dist + to_uniq
    return to_uniq


if __name__ == "__main__":

    usage = __doc__.split("\n\n\n")
    parser = argparse.ArgumentParser(
            formatter_class=argparse.RawDescriptionHelpFormatter,
            description=usage[0], epilog=usage[1])

    parser.add_argument("target_dir", type=str, help="Root directory to search for symlinks")
    parser.add_argument("--not-dry", dest="dry", default=True,
        action="store_false", help="Whether to do a dry run or not [default: do a dry run]")

    args = parser.parse_args()

    count = 0
    for curdir, dirs, files in os.walk(args.target_dir):

        files = [path.join(curdir, x) for x in files]
        for f in [x for x in files if is_abs_link(x)]:

            link_canon = path.abspath(path.expanduser(f))
            target_canon = os.readlink(link_canon)

            target_rel = calc_relative(link_canon, target_canon)
            link_dir = path.dirname(link_canon)

            if not args.dry:

                # make sure link is writeable
                if os.access(link_canon, os.W_OK):
                    os.remove(link_canon)
                else:
                    print("Can not update '{0}'".format(link_canon))
                    continue

                # need +wx bits for writing files in directory
                if os.access(link_dir, os.W_OK) and os.access(link_dir, os.X_OK):
                    os.symlink(target_rel, link_canon)
                else:
                    print("Can not write symlink in '{0}'".format(link_dir))
                    continue

                print("Updated '{0}' to point to '{1}'".format(link_canon, target_rel))
                count += 1

            else:

                print("Symlink target: '{0}', link name: '{1}'".format(target_rel, link_canon))
                count += 1

    if not args.dry:
        print("Total updated symlinks:", count)
    else:
        print("Total symlinks to update:", count)