add_var.py

#!/usr/bin/env python

####
#
# Usage:
#     ./add_var.py [key] [value]
#
####

import re
import sys

replacement = sys.argv[1] + '\t' + sys.argv[2]
group = None
replaced = False
found_defaults_group = False
indent = ''
for line in open('haproxy.cfg'):

	if replaced:
		# we have finished replacements, nothing else needed
		print line,
		continue

	found_group = re.search('^(\S+).*',line)
	if found_group:
		# we found a new group
		new_group = found_group.group(1)
		if new_group == 'defaults':
			found_defaults_group = True
		elif group == 'defaults' and new_group != 'defaults' and not replaced:
			# we left the 'global' group without replacing something
			print indent + replacement
			replaced = True
		group = new_group
	elif found_defaults_group:
		found_indented_line = re.search('^(\s+)(.*)', line)
		if found_indented_line and len(found_indented_line.group(2).strip()) != 0:
			indent = found_indented_line.group(1)
			# we found a indented line
			val = found_indented_line.group(2)
			if val.startswith(sys.argv[1]):
				# the key in that line matches the replacement key
				print indent + replacement
				replaced = True
				continue
		elif replaced == False:
			# we got to a line that's neither a group nor an indented line
			# so print the replacement plus the line
			print indent + replacement
			replaced = True

	print line,