exec函数簇的作用:在进程的内部执行一个可执行文件。原进程将被取代,在旧的躯壳上注入了新的灵魂。若调用成功,由于原进程不复存在,所以不返回任何值;若调用失败,则返回-1,从原进程的调用点接着往下进行。fork()配合exec(),可以使得应用程序产生一个新进程。
main函数:
int main( int argc, char *argv[], char *envp[] );
第一个参数argc是运行时参数的个数,第二个参数argv用来存放运行时参数,第3个参数用来存放系统环境变量。
1 #include<stdio.h>
2 #include<unistd.h>
3
4 int main( int argc, char *argv[], char *envp[] ){
5 printf("### argc ###/n");
6 printf(" %d /n", argc);
7 printf("### argv ###/n");
8 while(*argv)
9 printf("%s/n", *argv++);
10 printf("### envp ###/n");
11 while(*envp)
12 printf("%s/n", *envp++);
13
14 return 0;
15 }
========================exec.c===========================
#include<unistd.h>
int main(){
int status = 0;
char *envp[] = {"PATH=/tmp", "USER=lei", "STATUS=testing", NULL};
char *argv_execv[]={"echo", "excuted by execv", NULL};
char *argv_execvp[]={"echo", "excuted by execvp", NULL};
char *argv_execve[]={"env", NULL};
if(fork() == 0){
if(execl("/bin/echo", "echo", "executed by execl", NULL) < 0)
perror("Err on execl");
}
if(fork() == 0){
if(execlp("echo", "echo", "executed by execlp", NULL) < 0)
perror("Err on execlp");
}
if(fork() == 0){
if(execle("/usr/lib/env", "env", "executed by execle", NULL, envp) < 0)
perror("Err on execle");
}
if(fork() == 0){
if(execv("/bin/echo", argv_execv) < 0)
perror("Err on execv");
}
if(fork() == 0){
if(execvp("echo", argv_execvp) < 0)
perror("Err on execvp");
}
if(fork() == 0){
if(execve("/usr/bin/env", argv_execve, envp) < 0)
perror("Err on execve");
}
wait(status) ;
}
====
explore@ubuntu:~/Documents/Linux C Programming/Process/exec$ cc exec.c
explore@ubuntu:~/Documents/Linux C Programming/Process/exec$ ./a.out
Err on execle: No such file or directory
excuted by execv
executed by execl
excuted by execvp
explore@ubuntu:~/Documents/Linux C Programming/Process/exec$ PATH=/tmp
USER=lei
STATUS=testing
excuted by execvp
executed by execlp
excuted by execv
PATH=/tmp
USER=lei
STATUS=testing
(对于这里的结果不解释)。