Tcl/Expect脚本中两子进程能否同时输出到stdout？相关问题求助

我编写了一个Expect脚本，流程如下：

• 启动子进程test1.py（模拟certbot）
• 解析其输出，提取数据后执行第二个子进程test2.py
• 最后向第一个进程发送回车

遇到两个问题：

1. 给test2.py添加日志输出后，用exec调用它时直接报错：

   while executing
   "exec ./test2.py "$SITE_DOMAIN" "$fileName" "$fileData""
   (file "./test.exp" line 23)
   

   删除test2.py的日志语句后恢复正常。
2. 将exec改为spawn后，报错消失，但第一个进程的后续输出（比如test1.py最后打印的done）无法显示，最终只看到test2.py的Upload complete输出。

最小复现文件 #

main.exp #

#!/usr/bin/expect
set SITE_DOMAIN $env(SITE_DOMAIN)
set SITE_EMAIL $env(SITE_EMAIL)

# Spawn the certbot process
spawn ./test1.py certonly -m "$SITE_EMAIL" --agree-tos --no-eff-email --force-renew --preferred-challenges http --manual -d "$SITE_DOMAIN" -d "www.$SITE_DOMAIN"
set certbot_spawn_id $spawn_id

# Expect the output starting with 40 hyphens and capture it
expect {
    -re {(?n)^(- ){39}-\r\nCreate a file containing just this data:\r\n\r\n([\w.-]+)\r\n\r\nAnd make it available on your web server at this URL:\r\n\r\n.+\/acme-challenge\/([\w.-]+)} {
        set fileData $expect_out(2,string)
        set fileName $expect_out(3,string)
    }
    timeout {
        "Error: output from certbot did not match the expected pattern"
        exit 1
    }
}

# Call a separate command with the parsed value
exec ./test2.py "$SITE_DOMAIN" "$fileName" "$fileData"

# Send Enter to the certbot process to confirm
send -i $certbot_spawn_id "\r"

# Wait for the certbot process to finish
expect eof

test1.py #

#!/usr/bin/env python
OUTPUT = """"
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Account registered.
Requesting a certificate for example.com and www.example.com

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Create a file containing just this data:

ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopq.rstuvwxyz01234567890ABCDEFGHIJKLMNOPQRSTUVW

And make it available on your web server at this URL:

http://example.com/.well-known/acme-challenge/ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopq

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
"""

print(OUTPUT)
thing = input()
print("done")

test2.py #

#!/usr/bin/env python
import logging
from time import sleep

logger = logging.getLogger(__name__)
logger.setLevel(logging.INFO)
logging.basicConfig()

logger.info("Uploading file to web server")
sleep(2)
logger.info("Upload complete")
sleep(1)

问题1：exec调用报错的修复 #

exec在Expect中会捕获子进程的标准输出和错误，默认情况下如果子进程有输出，exec会将其返回，但未显式处理时会触发错误（Expect认为这是非预期输出）。

有两种修复方式：

• 方法1：将输出重定向到终端（保留日志，适合调试）

  exec ./test2.py "$SITE_DOMAIN" "$fileName" "$fileData" >@stdout 2>@stderr
  

• 方法2：忽略所有输出（调试完成后可选）

  exec ./test2.py "$SITE_DOMAIN" "$fileName" "$fileData" >/dev/null 2>&1
  

问题2：spawn后无法看到第一个进程输出的修复 #

用spawn启动test2.py后，Expect的默认spawn_id会切换到新进程，后续的expect eof只会等待第二个进程结束，不会监听第一个进程的输出。

修复时需显式管理两个进程的spawn_id：

# 替换原exec语句为：
spawn ./test2.py "$SITE_DOMAIN" "$fileName" "$fileData"
set upload_spawn_id $spawn_id
# 等待test2.py执行完成
expect -i $upload_spawn_id eof

# 切回certbot进程，发送回车
send -i $certbot_spawn_id "\r"

# 等待certbot进程完成并捕获其输出
expect -i $certbot_spawn_id eof

内容的提问来源于stack exchange，提问作者soapergem