lvm2json - filter to format lvs as JSON

lvm2json

#!/usr/bin/python

"""
Filter accepting input in the form

    FIELD='VALUE' FIELD2='VALUE2' ...
    ...

NOTE: Apostrophes are hardcoded separators and `FIELD` may contain only
uppercase letters, digits and underscores.

NOTE: this does not handle backslash escape sequences properly.

Returning JSON representation as list of dictionaries with list items
correspond to lines, dictionary to `(FIELD, VALUE)` pairs:

    [
      {
        "FIELD": "VALUE",
        "FIELD2": "VALUE2",
        ...
      },
      ...
    ]


This is useful with `lvs`, `pvs`, `vgs` and `dmsetup info -c` commands as following:

    lvs --noheadings --nameprefixes -avo+devices | lvm2json
    dmsetup info -c --noheadings --nameprefixes | lvm2json

Tested with ancient LVM2-2.02.88 on RHEL5.


The heart is near single line `lvm_parse` function.


"""

import sys
import json

import re
import subprocess


_KEY_VALUE_RE=re.compile("([A-Z0-9_]*)='(([^\\\\']|\\\\.)*)'")


def lvm_parse(s):
  """
  Parse output of lvs, pvs or vgs with `--nameprefixes --noheadings` and return list of dictionaries.
  """
  lines=s.splitlines()
  return [dict((match[0], match[1]) for match in _KEY_VALUE_RE.findall(line)) for line in lines]


if __name__ == "__main__":
  if len(sys.argv) > 1:
    a1 = sys.argv[1]
    if a1 == "-h" or a1 == "--help":
      print __doc__
    else:
      print >> sys.stderr, "Unknown options: %r" % sys.argv
      sys.exit(1)
  else:
    print json.dumps(lvm_parse(sys.stdin.read()), indent=2)