man/90-rearrange-path.py

   1 #!/usr/bin/env python3
   2 # SPDX-License-Identifier: MIT-0
   3
   4 """
   5
   6 Proof-of-concept systemd environment generator that makes sure that bin dirs
   7 are always after matching sbin dirs in the path.
   8 (Changes /sbin:/bin:/foo/bar to /bin:/sbin:/foo/bar.)
   9
  10 This generator shows how to override the configuration possibly created by
  11 earlier generators. It would be easier to write in bash, but let's have it
  12 in Python just to prove that we can, and to serve as a template for more
  13 interesting generators.
  14
  15 """
  16
  17 import os
  18 import pathlib
  19
  20 def rearrange_bin_sbin(path):
  21     """Make sure any pair of …/bin, …/sbin directories is in this order
  22
  23     >>> rearrange_bin_sbin('/bin:/sbin:/usr/sbin:/usr/bin')
  24     '/bin:/sbin:/usr/bin:/usr/sbin'
  25     """
  26     items = [pathlib.Path(p) for p in path.split(':')]
  27     for i in range(len(items)):
  28         if 'sbin' in items[i].parts:
  29             ind = items[i].parts.index('sbin')
  30             bin = pathlib.Path(*items[i].parts[:ind], 'bin', *items[i].parts[ind+1:])
  31             if bin in items[i+1:]:
  32                 j = i + 1 + items[i+1:].index(bin)
  33                 items[i], items[j] = items[j], items[i]
  34     return ':'.join(p.as_posix() for p in items)
  35
  36 if __name__ == '__main__':
  37     path = os.environ['PATH'] # This should be always set.
  38                               # If it's not, we'll just crash, which is OK too.
  39     new = rearrange_bin_sbin(path)
  40     if new != path:
  41         print('PATH={}'.format(new))