Journal printer with custom formatting

journalprintf.py

#!/usr/bin/env python

'''
A journal reader which offers custom message formatting on output.

Example:

    ./journalprintf \
        '{__REALTIME_TIMESTAMP} {_HOSTNAME} {_SYSTEMD_UNIT} {_COMM}[{_PID}]: {MESSAGE}' \
        _SYSTEMD_UNIT=dnsmasq.service \
        _SYSTEMD_UNIT=systemd-networkd.service

Known limitations:
    If a field is requested field is missing from the journal entry, the field
    will be skipped entirely, rather than being replaced with something/nothing.
'''

import sys
from systemd import journal

with journal.Reader() as j:
    j.this_boot()

    for m in sys.argv[2:]:
        j.add_match(m)

    for entry in j:
        try:
            print(sys.argv[1].format(**entry))
        except KeyError as e:
            pass