system(), exec函数族， fork函数用法说明

启动一个新线程的方式：

• system()

  该函数经常用来在C程序中调用shell脚本或者命令行程序.

  特点：

  效率低下，首先需要创建一个shell, 然后配置shell环境，之后再执行相应的命令。

  对shell环境的依赖很大。

• exec() 函数族

  也用来创建新的进程，但会替换原先的进程

  int execl(const char *path, const char *arg0, …, (char *)0);

  int execp(const char *file, const char *arg0, …, (char *)0);

  int execle(const char *path, const char *arg0, …, (char *)0, char *const envp[]);

  int execv(const char *path, const char *argv[]);

  int execvp(const char *file, const char *argv[]);

  int execve(const char *path, const cha *argv[], char *const envp[])

• fork()

  复制原先的进程环境，从而创建一个新的子进程0

示例：

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <unistd.h>

#include <sys/types.h>

#include <sys/wait.h>

#include <signal.h>

#include "../main/basic_utilits.h"

void system_demo()

{

    printf("Run a script file in C envirenment\n");

    system("../shell/mkPasswd.sh 10");

    system("ps aux | awk '{print $11}' | sort | uniq -c | sort -nr | awk '{print $2}' | head");

    printf("shell script over\n");

}

void exec_funcs()

{

    char *const ps_argv[] =

    {"ps", "ax", 0};

    char *const ps_envp[] =

    {"PATH=/bin:/usr/bin:/usr/local/bin:/sbin", "TERM=console", 0};

    execl("/bin/ps", "ps", "-ax", NULL);

    execlp("ps", "ps", "ax", NULL);

    execle("/bin/ps", "ps", "ax", NULL, ps_envp);

    execv("/bin/ps", ps_argv);

    execvp("ps", ps_argv);

    execve("/bin/ps", ps_argv, ps_envp);

}

void fork_demo()

{

    pid_t pid;

    int exit_code = 0;

    char *message = NULL;

    int count = 0;

    int i = 0;

    pid = fork();

    switch(pid){

        case -1:

            printf("fork_demo: fork error\n");

            break;

        case 0:

            exit_code = 37;

            count = 10;

            message = "This is child process\n";

            break;

        default:

            exit_code = 0;

            count = 5;

            message = "This is parent process\n";

            break;

    }

    for(i=0;i<count;i++){

        printf("%s", message);

        my_msleep(500);

    }

    if(pid){

        int stat_child = 0;

        pid_t child_pid;

        //child_pid = wait(&stat_child); //获取的退出码需要使用特定的宏函数进行操作

        waitpid(pid, &stat_child, 0);

        printf("child pid : %d  stat_code: %d\n", pid, WEXITSTATUS(stat_child));

    }

    printf("exit code : %d\n", exit_code);

    exit(exit_code);

}