Find & fix bad Symlinks in Dropbox folder

droplinks.py

#!/usr/bin/env python

import sys
import optparse
from os import path
import subprocess

OLD_PYTHON_VERS = "2.7.5"
NEW_PYTHON_VERS = "2.7.8_1"
# first char index of filename, from my ls:
FILE_POS = 49
LINK_STRING = ' -> '

usage = """usage: %prog [options]
       expects input on stdin from "ls -lah" (or "ls -la", or "ls -l")
       example:
           $ find . -type l -exec ls -lah {}\; | %prog --dry-run
       after reviewing all the settings, and convincing yourself that you
       are helped by the re-linking commands displayed, then:
           $ find . -type l -exec ls -lah {}\; | %prog
       is appropriate.
"""
parser = optparse.OptionParser(usage=usage)
parser.add_option('-n', '--dry-run',
                  action="store_true", default=False,
                  help="dry run, prints what commands would be run.")
parser.add_option('--from', dest="from_string",
                  action="store", type="string", default=OLD_PYTHON_VERS,
                  help="string to convert from, in broken link target.\ndefault: {s}".format(s=OLD_PYTHON_VERS))
parser.add_option('--to', dest="to_string",
                  action="store", type="string", default=NEW_PYTHON_VERS,
                  help="string to convert to, the corrected link target.\ndefault: {s}".format(s=NEW_PYTHON_VERS))
parser.add_option('--file-pos',
                  action="store", type="int", default=FILE_POS,
                  help="character position of filename (e.g. from \"ls\")\ndefault: {i}".format(i=FILE_POS))
parser.add_option('--link-string',
                  action="store", type="string", default=LINK_STRING,
                  help="""string separating link from target.
                  default: \"{s}\"""".format(s=LINK_STRING))
opt, args = parser.parse_args()

# for zero-based list indexes:
opt.file_pos -= 1

# call or dry-run:
if opt.dry_run is True:
    do_call = lambda cmd,trg,lnk:\
                sys.stdout.write(cmd+" {t} {l}".format(t=trg, l=link) + '\n')
else:
    do_call = lambda cmd,trg,lnk:\
                subprocess.check_output(cmd.split(), trg, lnk,
                                 stderr=subprocess.STDOUT)

for line in sys.stdin:
    # doesn't look like a link:
    if opt.link_string not in line:
        continue
    # last char is newline, which we don't want
    link, target = line[opt.file_pos:-1].split(opt.link_string)
    if target[0] != "/":
        realtarget = path.join(path.dirname(link), target)
        if not path.exists(realtarget):
            print "Failed link to a relative target: {t}".format(t=target)
            print " -> link:", link
    elif not path.exists(target):
        print "Missing target: {t}".format(t=target)
        if opt.from_string in target:
            ntarget = target.replace(opt.from_string, opt.to_string)
            if path.exists(ntarget):
                do_call("ln -fsv", ntarget, link)
            else:
                print("Failed link: {l}".format(l=link))

Oh, and no guarantees if you're using python2.6 or older (although I tried to make it 2.6 compatible).