Linux PWD instruction C implementation

Linux pwd command C realizes the whole idea

• To implement the PWD command:

• Enter PWD at the command line: Displays the path that is now located.
  

• Study the system calls required to implement PWD

• We can get the system call function information we need through the man command and the grep command.

• Mans ChDir
  

• The directory is a kind of file, this file is special, it is stored in a corresponding table, that is, the file name and the corresponding relationship table of I node, and I node is the structure of the record details of this file, such as file size, attributes, permissions, the existence of the hard disk block and so on. To create a file in a directory is to add a corresponding relationship in this table, using a file is based on the I node to determine the actual storage location of the hard disk.

1. can be done by

   readdir(".")

   To get the current directory.

2. cd ..

Cd

command to return to the parent directory, and then

readdir(".");

To read the current directory and execute it sequentially.

1. So by implementing

   cd

   command, you can resolve

   pwd

   Command

2. Pass

   man -k chage | grep dir

   = = Available ChDir implementation = =

3. Run the view in the root directory

   "."

".."

Node number of the I nodes. = = can be used as the terminating condition of the loop = =.

1. ls -i -a .

   To view the I node value.

To summarize, it is:

1. Find the I-node in this directory

2. Go to the parent directory and find the file name of the I-node

3. Cycle the above process until it reaches the root

Pseudo code

     定义一个char数组用来保存当前目录的绝对路径；     递归：    调用函数chdir()来改变当前程序的工作路径；（返回上一级）    if(返回的指针==NULL)        调用函数中存在错误，输出错误警告；    else        直接打印结果    

Code implementation

Detailed code:

#include <stdio.h> #include <sys/types.h> #include <sys/stat.h> #include <dirent.h>ino_t get_  Inode (char*), void Printpathto (ino_t), void Inum_to_name (ino_t,char*,int), int main () {Printpathto (Get_inode ("."));    Print path to here Putchar (' \ n '); return 0;}    void Printpathto (ino_t this_inode) {ino_t my_inode;    Char Its_name[bufsiz]; /* If the I-node in this directory is different from the parent directory, that is, this directory is not the root directory */if (Get_inode ("..")!         =this_inode) {chdir ("..");        Enter the parent directory Inum_to_name (THIS_INODE,ITS_NAME,BUFSIZ);        My_inode = Get_inode (".");        Printpathto (My_inode);    printf ("/%s", its_name);    }}void inum_to_name (ino_t inode_to_find,char* namebuf,int buflen)//Find the file name of the I-node and place it in the character array {dir* dir_ptr;    struct dirent* direntp;    Dir_ptr = Opendir (".");        if (dir_ptr = = NULL) {perror (".");    Exit (1);  } while ((DIRENTP = Readdir (dir_ptr)) = NULL) {if (Direntp->d_ino = = Inode_to_find) {          strncpy (Namebuf,direntp->d_name,buflen);            Namebuf[buflen-1] = ' + ';            Closedir (DIR_PTR);        Return    }} fprintf (stderr, "error looking for inum% d\n", inode_to_find); Exit (1);}    ino_t Get_inode (char* fname)//based on the file name, returns the-I node {struct STAT info;        if (stat (fname, &info) = =-1) {fprintf (stderr, "cannot stat");        Perror (fname);    Exit (1); } return Info.st_ino;}

Linux pwd instruction C implementation