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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 
   
    #include 
    
     #include 
     
      #include 
      
       #include 
       
        #include 
        
         #include 
         
          #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
         
        
       
      
     
    
   

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