50-static-ip.yaml_template

network:
  version: 2
  renderer: networkd
  ethernets:
    enp3s0:
      addresses:
        - @@IP_SUBNET@@
      gateway4: @@GATEWAY@@
      nameservers:
          addresses: [@@DNS@@]

example.conf_template

# This is a very simpelistic example file
bind_addr=@@SERVER_ADDR@@

placeholder_mover.py3

#!/usr/bin/python3
# This script is intended to allow easier rollout of software to multiple servers
# that each have a slightly diffrent configuration. There also need to be
# template configuration files provided, that have placeholders in the places 
# where the values need to be inserted. The placeholder will need to have the form
# @@PLACEHOLDER_NAME@@.
# To work it first asks the user for input, then does some light processing on the
# user inputs. After that it copies files while replacing the placeholders. At the
# end it executes some shell commands.


# This is the place where the values the user will be asked for are defined.
# name => internal name for the placeholder
# prompt => the text displayed to the user when asked for this placeholder value
# regex => regex used for validation of user input
# repeated (optional) => indicates, that the user can input multiple values 
# break (required if repeated) => regex for what needs to be input during 'repeated' 
# values to get to the next prompt
# start (optional, only used if repeated) => string to prepend before any 
# repeated values are put into string form
# seperator (optional, only used if repeated) => string to insert between 
# repeated values for string form
# end (optional, only used if repeated) => string to append after all
# repeated values are put into string form

placeholders = [
		{
			'name':'IP_SUBNET',
			'prompt':'IPv4 in CIDR notation: ',
			'regex':r'\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\/\d{1,2}',
		},
		{
			'name':'GATEWAY',
			'prompt':'IPv4 of the Default Gateway: ',
			'regex':r'\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}'
		},
		{
			'name':'DNS',
			'prompt':'IPv4 of the DNS Servers, use the empty string to terminate: ',
			'regex':r'\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}',
			'repeated': True,
			'seperator':',',
			'break':r''
		}
	]

# This is where some light processing for placeholders is defined. It takes a 'src'
# placeholder and writes whatevery is in the first capture group of the 'regex' to
# write into the 'dst' placeholder.
pholders_processing = [
		{
			'src':'IP_SUBNET',
			'dst':'IP',
			'regex':r'(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\/\d{1,2}'
		}
	]

# Here the source and destination for files to be copied is defined. 
# You also need to define what placeholders to use in a simple list of strings.
# Additionally to strings tuple pairs can be put in, an example is:
# ('IP', 'SERVER_ADDR') that can be read as 'use the IP placeholder, but for this
# file name it SERVER_ADDR'.
files = [
		{
			'src':'50-static-ip.yaml_template',
			#Normally the destination for this would be set to /etc/netplan/50-static-ip.yaml
			'dst':'50-static-ip.yaml',
			'placeholders': ['IP_SUBNET', 'GATEWAY', 'DNS']
		},
		{
			'src':'example.conf_template',
			'dst':'example.conf',
			'placeholders': [('IP', 'SERVER_ADDR')]
		}
	]

# This defines a list of commands to be ran after everything else was processed.
# The commands will be executed in the order defined here.
post_commands = [
		['echo', 'Executed the command!']
	]

import re
import subprocess

replacments = dict()

for p in placeholders:
	r = re.compile(p['regex'])
	repeated = p.get('repeated') and p.get('break') is not None
	if repeated:
		b = re.compile(p['break'])
		l = list()
	while True:
		prompt = p['prompt']
		tmp = input(f'{p.get("prompt")} ')
		if r.fullmatch(tmp):
			if repeated:
				l.append(tmp)
			else:
				replacments[p['name']] = tmp
				break
		if repeated and b.fullmatch(tmp):
			if p.get('start') is None:
				p['start'] = ''
			if p.get('seperator') is None:
				p['seperator'] = ''
			if p.get('end') is None:
				p['end'] = ''
			tmp = p['start']
			first = True
			for x in l:
				if not first:
					tmp += p['seperator']
				first = False
				tmp += x
			tmp += p['end']
			replacments[p['name']] = tmp
			break

for p in pholders_processing:
	if replacments.get(p.get('src')) is not list:
		r = re.compile(p['regex'])
		m = r.fullmatch(replacments.get(p.get('src')))
		if m:
			replacments[p.get('dst')] = m.groups()[0]

for file in files:
	cur_placeholders = dict()
	for x in file.get('placeholders'):
		if type(x) is str:
			cur_placeholders[x] = replacments.get(x)
		elif type(x) is tuple:
			cur_placeholders[x[1]] = replacments.get(x[0])
	with open(file.get('src'), 'rt') as fi:
		with open(file.get('dst'), 'wt') as fo:
			tmp = fi.read()
			for p, r in cur_placeholders.items():
				tmp = tmp.replace(f'@@{p}@@', r)
			fo.write(tmp)

	print(f"moved '{file.get('src')} to '{file.get('dst')}'")

for cmd in post_commands:
	r = subprocess.run(cmd, stdout=subprocess.PIPE)
	print(r.stdout.decode('utf-8'))