man: add systemd.environment-generator(7) with two examples

v2:
  - add example files to EXTRA_DIST
v3:
  - rework for the new scheme where nothing is written to disk
v4:
  - use separate dirs for system and user env generators

1 files changed, 40 insertions, 0 deletions

diff --git a/man/90-rearrange-path.py b/man/90-rearrange-path.py
new file mode 100755
index 0000000000..c6ff32210f
--- /dev/null
+++ b/man/90-rearrange-path.py
@@ -0,0 +1,40 @@
+#!/usr/bin/python3
+
+"""
+
+Proof-of-concept systemd environment generator that makes sure that bin dirs
+are always after matching sbin dirs in the path.
+(Changes /sbin:/bin:/foo/bar to /bin:/sbin:/foo/bar.)
+
+This generator shows how to override the configuration possibly created by
+earlier generators. It would be easier to write in bash, but let's have it
+in Python just to prove that we can, and to serve as a template for more
+interesting generators.
+
+"""
+
+import os
+import pathlib
+
+def rearrange_bin_sbin(path):
+    """Make sure any pair of …/bin, …/sbin directories is in this order
+
+    >>> rearrange_bin_sbin('/bin:/sbin:/usr/sbin:/usr/bin')
+    '/bin:/sbin:/usr/bin:/usr/sbin'
+    """
+    items = [pathlib.Path(p) for p in path.split(':')]
+    for i in range(len(items)):
+        if 'sbin' in items[i].parts:
+            ind = items[i].parts.index('sbin')
+            bin = pathlib.Path(*items[i].parts[:ind], 'bin', *items[i].parts[ind+1:])
+            if bin in items[i+1:]:
+                j = i + 1 + items[i+1:].index(bin)
+                items[i], items[j] = items[j], items[i]
+    return ':'.join(p.as_posix() for p in items)
+
+if __name__ == '__main__':
+    path = os.environ['PATH'] # This should be always set.
+                              # If it's not, we'll just crash, we is OK too.
+    new = rearrange_bin_sbin(path)
+    if new != path:
+        print('PATH={}'.format(new))