parse a profile

[Cameron Simpson]

On 18Feb2012 18:43, MRAB <python at mrabarnett.plus.com> wrote:
| On 18/02/2012 16:34, Jason Friedman wrote:
| > I have a file I use for shell scripts that looks like this:
| >
| > export VAR1=/path/to/dir
| > export VAR2=7
| > export VAR3=${VAR1}/further/path
| > # comment
| > . /another/file
| >
| > And a file /another/file:
| > export VAR4=database-name
| >
| > Is there an existing package that will read such a file and return a
| > dictionary like this:
| > {
| >      'VAR1': '/path/to/dir',
| >      'VAR2': 7,
| >      'VAR3': '/path/to/dir/further/path',
| >      'VAR4': 'database-name',
| > }
| 
| I would probably do something like this:
| 
| import re
| 
| # Parse the file into a dict.
| with open(path) as f:
|      d = dict(re.findall(r"(?m)^export (VAR\d+)=(.*)", f.read()))
| 
| # Expand any references.
| for key, value in d.items():
|      d[key] = re.sub(r"\$\{(VAR\d+)\}", lambda m: d[m.group(1)], value)

Which fails on the ". /anther/file" step, alas. Jason's point is
probably that it may be arbitrary shell.

I suspect I would write a shell wrapper like this:

  #!/bin/sh
  exec 3>&1 1>&2
  . /path/to/jason/s/file
  exec 1>&3 3>&-
  env

then from inside Python call the shell to run the wrapper.
Read the output of "env" and diff it against os.environ.
Populate the dictionary with the values that have changed.

Crude untested sketch:

  newvars = {}
  for envline in subprocess.blah(... run the wrapper script above ...):
    if not envline.endswith('\n'):
      raise ValueError("unexpected EOF")
    envline = envline[:-1]
    try:
      var, value = line.split('=', 1)
    except ValueError:
      # ouch!
      continue
    oldvalue = os.environ.get(var)
    if oldvalue is None or oldvalue != value:
      newvars[var] = value

You can put the wrapper script as a single inline piece of shell to
avoid the separate file once debugged.

Just a thought. Cheers,
-- 
Cameron Simpson <cs at zip.com.au> DoD#743
http://www.cskk.ezoshosting.com/cs/

[...] post-block actions should be allowed everywhere, not just on
subroutines. The ALWAYS keyword was agreed upon as a good way of doing
this, although POST was also suggested. This lead to the semi-inevitable
rehash of the try- catch exception handling debate. According to John
Porter, "There is no try, there is only do. :-)"
- from the perl6 development discussion