<UNIX advanced programming> note Chapter1

The OS is strictly software and provides resources and app running environment for computers. It is called the kernel.

The kernel interface is called as system call. Then the library function encapsulates the system call. shell is a special app that provides an interface for running other programs.

Shell is a command line interpreter. It reads the input and executes the command.

The UNIX file system is composed of directory and file. The directory starts from root and is named /.

File Attribute refers to the type, size, owner, permission, and modification time. Stat and fstat returned File Attribute structure.

For example:

2. File Name

Only/and null cannot appear in the file name. Because/is used to separate the component path name, null is used to terminate a path name.

If you create a new directory, two file names are automatically created ..

Point refers to the current directory,... refers to the upper-level directory.

3. Path Name

One or more/form the path name.

Starting with "/" indicates the relative path. Otherwise, it is an absolute path. In fact, relative paths are often used.

Practice:

1. Listing all files in the directory is to implement the LS function.

#include <dirent.h>#include "stdio.h"#include "stdlib.h"int main(int argc, char** argv){    if (argc != 2){        printf("usage: ls dir_name\n");        return 1;    }    DIR* dp = opendir(argv[1]);    if (NULL == dp){        printf("can't open %s\n", argv[1]);        return 1;    }    printf("load dir success\n");    struct dirent* dirp = NULL;    while ((dirp = readdir(dp)) != NULL)        printf("%s ", dirp->d_name);    printf("\n");    closedir(dp);    return 0;}

The results show that... And... are indeed valid directories. The printed results are unordered. The ls results are ordered.

Exit (0) indicates that the program Exits normally. 1-255 indicates the error code.

1.5 Input and Output

FD is a non-negative integer. It indicates the file being accessed by a specific process by the kernel.

Each time the shell is opened, three default FD are opened: stdin stdout stderror

In addition, shell can be easily redirected.

3) No buffer Io

Open read close write lseek provides Io without buffering

Code:

#include "stdio.h"#include "unistd.h"int main(){    int n = 0;    const int maxLen = 4096;    char buff[maxLen];    while ((n == read(STDIN_FILENO, buff, maxLen)) > 0){        if (write(STDOUT_FILENO, buff, n) != n){            printf("error\n");            exit(1);        }    }        exit(0);}

This code is not very understandable. Let's see it tomorrow.

Learn this.