dup2 function

The current system process information in print to file

Command line: ps aux> out information ps will get redirected to file out

 

Use dup2 complete file in the program.

int dup2(int oldfd,int newfd);

/***
dup2.c
***/
#include<stdio.h>
#include<fcntl.h>
#include<unistd.h>
#include<stdlib.h>

int main()
{
    int fd;
    
    fd = open("ps.out",O_WRONLY|O_CREAT|O_TRUNC,0644);
    if(fd < 0)
    {
        perror("open ps.out error");
        exit(1);
    }
    dup2(fd,STDOUT_FILENO); //dup2(3,1);  fd,stdout
    execlp("ps","ps","ax",NULL);
    //close(fd);
    return 0;
}

operation result:

ubuntu1604 @ ubuntu: ~ / wangqinghe / linux / 20190806 $ ls -l ps.out

-rw-r--r-- 1 ubuntu1604 ubuntu1604 13121 8月   6 14:00 ps.out