echo expect脚本是非确定性的

Question

以下期望/代码对有时只能起作用：

1. 简单的cpp echo程序：

    #include <iostream>
    #include <string>
   
    using namespace std;
   
    int main()
    {
       string buffer;
       while (1)
       {
           getline(cin, buffer, '\n');
           if (cin.eof())
               break;
           cout<<buffer<<endl;
       }
       return 0;
    }
   

2. 期待剧本

   #!/usr/bin/expect
   
   spawn ./echo
   
   exp_internal 1
   
   set timeout 1
   
   send "a\n"
   expect {
       -re {^a\r\n$}
   }
   

3. 成功匹配：

   spawn ./echo
   send: sending "a\n" to { exp6 }
   Gate keeper glob pattern for '^a\r\n$' is 'a
   '. Activating booster.
   
   expect: does "" (spawn_id exp6) match regular expression "^a\r\n$"? Gate "a\r\n"? gate=no
   a
   
   expect: does "a\r\n" (spawn_id exp6) match regular expression "^a\r\n$"? Gate "a\r\n"? gate=yes re=yes
   expect: set expect_out(0,string) "a\r\n"
   expect: set expect_out(spawn_id) "exp6"
   expect: set expect_out(buffer) "a\r\n"
   

4. 失败匹配：

   spawn ./echo
   send: sending "a\n" to { exp6 }
   Gate keeper glob pattern for '^a\r\n$' is 'a
   '. Activating booster.
   
   expect: does "" (spawn_id exp6) match regular expression "^a\r\n$"? Gate "a\r\n" gate=no
   a
   a
   
   expect: does "a\r\na\r\n" (spawn_id exp6) match regular expression "^a\r\n$"? Gate "a\r\n"? gate=yes re=no
   expect: timed out
   

我不明白为什么在某些跑步中我得到双线“a”，有些跑步我得到单曲？我会假设期望挂钩产生的过程，以便发送将所有内容传递给stdin，期望从stdout获取所有内容。

任何澄清都将不胜感激。