程序在execvp（command.argv [0]，command.argv） [英] program stops after execvp( command.argv[0], command.argv)

问题描述

我正在写一个小的shell程序，它接受一个命令并执行它。如果用户输入无效的命令，if语句返回-1。如果命令正确，它执行命令，但是一旦它执行命令程序结束。我做错了什么是不执行代码行之后呢？我已经测试execvp（command.argv [0]，command.argv）与ls和cat命令，所以我很确定它的工作原理。这里是我的代码。

I am writing a small shell program that takes a command and executes it. If the user enters a not valid command the if statement returns a -1. If the command is correct it executes the command, however once it executes the command the program ends. What am I doing wrong that is does not execute the lines of code after it? I have tested execvp( command.argv[0], command.argv) with ls and cat commands so I am pretty sure it works. Here is my code.

  int shell(char *cmd_str ){
  int commandLength=0;
  cmd_t command;
  commandLength=make_cmd(cmd_str,  command);
  cout<< commandLength<<endl;
  cout << command.argv[0]<< endl;
  if( execvp( command.argv[0], command.argv)==-1)
//if the command it executed nothing runs after this line
  {
    commandLength=-1;

}else
{
  cout<<"work"<<endl;
}

  cout<< commandLength<<endl;
   return commandLength;


}

推荐答案

从 execvp（3）的手册页

exec（）函数系列用
a替换当前的过程映像

The exec() family of functions replaces the current process image with a new process image

因此，您当前的过程映像将被您的命令的映像覆盖！因此，您需要使用 fork + exec 组合，以便您的命令在子进程中执行，并且您的当前进程作为父进程安全地继续！

So your current process image is overwritten with the image of your command! Hence you need to use a fork+exec combination always so that your command executes in the child process and your current process continues safely as a parent!

在较轻的音符上，我想用图片来说明问题，因为一个图片说一千个字。没有进攻意图:)：）

On a lighter note I want to illustrate the problem with a picture as a picture speaks a thousand words. No offence intended :) :)

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