用execv调用'ls' [英] Calling 'ls' with execv

问题描述

我是系统调用和C编程的新手，正在从事大学作业.

I am new to system calls and C programming and am working on my university assignment.

我想调用'ls'命令并让它打印目录.

I want to call the 'ls' command and have it print the directory.

我所拥有的:(我添加了注释，以便您可以看到通过每个变量看到的内容.

What I have: (I have added comments in so you can see what I see coming through each variable.

int execute( command* cmd ){

  char full_path[50];
  find_fullP(full_path, p_cmd); 
  //find_fullP successfully updates full_path to /bin/ls
  char* args[p_cmd->argc];
  args[0] = p_cmd->name;
  int i;
  for(i = 1; i < p_cmd->argc; i++){
      args[i] = p_cmd->argv[i];
  }

/*
 * this piece of code updates an args variable which holds arguments 
 * (stored in the struct) in case the command is something else that takes 
 * arguments. In this case, it will hold nothing since the command 
 * will be just 'ls'.
 */

  int child_process_status;
  pid_t child_pid;
  pid_t pid;

  child_pid = fork();

  if ( child_pid == 0 ) {
      execv( full_path, args );
      perror("fork child process error condition!" );
  }

  pid = wait( &child_process_status );
  return 0;
}

我什么都没看见而且很困惑，知道吗?

I am not seeing anything happening and am confused, any idea?

推荐答案

这是使用execv调用ls的最小程序.注意事项

Here's the minimal program that invokes ls using execv. Things to note

• args的列表应将可执行文件作为第一个arg
• args的列表必须以NULL终止
• 如果正确设置了args，则可以将args[0]作为第一个参数传递给execv

• the list of args should include the executable as the first arg
• the list of args must be NULL terminated
• if the args are set up correctly, then args[0] can be passed as the first parameter to execv

#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

int main( void )
{
    int status;
    char *args[2];

    args[0] = "/bin/ls";        // first arg is the full path to the executable
    args[1] = NULL;             // list of args must be NULL terminated

    if ( fork() == 0 )
        execv( args[0], args ); // child: call execv with the path and the args
    else
        wait( &status );        // parent: wait for the child (not really necessary)

    return 0;
}

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