packer buildしてできたamiだけ取得(packerの出力変わると使えない)

#!/usr/bin/env python

import subprocess
import re

def run(cmd):
    p = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
    stdout = []
    while True:
        line = p.stdout.readline()
        stdout.append(line)
        if not line and p.poll() is not None:
            for text in stdout:
                match = re.search('ap-northeast-1:\s{1}(.*)', str(text.decode("utf-8")))
                if match:
                    print(match.group(1), end = "")
            break
    return ''.join(str(stdout))

if __name__ == '__main__':
    run("packer build -var-file=var.json template.json") 

プレースホルダを含んだtfを使うなど

python exec_packer.py | xargs -I{} sed -e 's/{{AMI_ID}}/{}/g' test.tf > test_e.tf