#include <unistd.h>extern char **environ;int execl(const char *path,const char *arg, ...);int execlp(const char *file,  const char *arg, ...);int execle(const char *path,const char *arg, ..., char * const envp[]);int execv(const char *path,char *const argv[]);int execvp(const char *file, char *const argv[]);int execve(const char *file, char *const argv[], char *const envp[]);exec函数出错返回-1，成功不返回

execve是系统函数，其他都是库函数

#include <stdlib.h>int system(const char *command)返回:成功返回命令状态，出错返回-1功能：简化exec函数使用system函数内部构建一个子进程，由子进程调用exec函数等同于/bin/bash -c "cmd" 或者 exec("bash","-c","cmd")

#include <unistd.h>#include <stdlib.h>#include <stdio.h>char *cmd1="/bin/date";int main(void){    system("clear");    system(cmd1);        return 0;}

#include <sys/types.h>#include <sys/wait.h>#include <errno.h>#include <unistd.h>int system(const char * cmdstring){    pid_t pid;    int status;    if(cmdstring == NULL){                   return (1);    }    if((pid = fork())<0){            status = -1;    }    else if(pid = 0){        execl("/bin/sh", "sh", "-c", cmdstring, (char *)0);        exit(127);         }    else{            while(waitpid(pid, &status, 0) < 0){                if(errno != EINTER){                    status = -1;                    break;                }            }        }        return status;}