1. Everything is a file in Linux

• 정규 파일뿐만 아니라, 디바이스, 소켓, 메모리, 프로세스 모두 파일로 표현됨

1. Terminal 1

1. dev/pts/6

2. Terminal 2

2. dev/pts/7c

2. Cat command

1. 코드

#include <stdio.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#define MAX_BUF 64

int main(int argc, char * argv[]){

	int fd, read_size, write_size;
	char buf[MAX_BUF];

	if(argc !=2)
	{
		printf("USAGE: %s file name\n", argv[0]);
		exit(-1);
	}

	fd = open(argv[1], O_RDONLY);

	if(fd<0)
	{
		printf("Can't open file %s", argv[1]);
		exit(-1);
	}

	while(1){
		read_size= read(fd,buf,MAX_BUF);
		if(read_size==0){
			break;
		}
		write_size = write(STDOUT_FILENO,buf,read_size);
	}

	close(fd);
	return 0;
}

2. 동작 모습

>

3. Cat commant with redirection

1. 코드

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#define BUF_SIZE 1024

int main(int argc, char* argv[])
{
    int fd, rfd, read_size, write_size;
    char buf[BUF_SIZE];
    if (argc != 3)
    {
        perror("argu");
        exit(1);
    }
    fd = open(argv[1], O_RDONLY);
    if (fd < 0)
    {
        perror("openfile");
        exit(1);
    }
    rfd = open(argv[2], O_RDWR | O_CREAT, 0641);
    dup2(rfd, STDOUT_FILENO);
    while (1)
    {
        read_size = read(fd, buf, BUF_SIZE);
        if (read_size == 0)
            break;
        write_size = write(STDOUT_FILENO, buf, read_size);
    }
    close(fd);
    close(rfd);
    return 0;
}

2. 동작 모습