pacman_rollback.py

#!/usr/bin/env python

import re

last_lines = lines = None

with open('/var/log/pacman.log') as log_file:
    for line in log_file:
        if re.search(r'\btransaction started\b', line):
            lines = []
        elif re.search(r'\btransaction completed\b', line):
            last_lines = lines
            lines = None
        elif lines is not None:
            lines.append(line.strip())

to_upgrade = []
to_remove = []

for line in last_lines:
    m = (re.search(r' removed (.+?) \((.+?)\)$', line) or
         re.search(r' upgraded (.+?) \((.+?) -> .+?\)', line))
    if m:
        to_upgrade.append('/var/cache/pacman/pkg/{}-{}-*.pkg.tar.xz'.format(*m.groups()))

    m = re.search(r' installed (.+?) \(.+?\)$', line)
    if m:
        to_remove.append('{}'.format(*m.groups()))

sep = ' \\\n '
print('sudo pacman -U' + ''.join(sep + pkg for pkg in to_upgrade))
print('sudo pacman -R' + ''.join(sep + pkg for pkg in to_remove))