ls -- list directory contents

1. How to read entry and show directory contents?
2. How to get file properties and how to show them?
3. Give you a name, how to tell whether it is a file or a directory?

Hint: The directory is a special kind of file. It contains a lot of records, each with a uniform standard format. The content of each record represents a file or directory. The directory can be opened by a standard file function. The directory is not an unformatted text but contains a certain data structure.

1. man -k direct | grep read # learn how to read dir file
2. read mannul of readdir and get other information.
3. learn about opendir/readdir/closedir/dirent.h and so on.
4. Write your own ls command!

    open directory
+-> read entry            - end of dir? -+
|_  display file info                    |
    close directory     <----------------+

see ls1.c

Some other file attributes is not stored in dirent struct.

1. get file stat, see filestat.c
2. change the integer file mode into string like -rw-rw-r--. Use bit masking.
3. change user/group id into username and groupname.

You can do by these steps: +--> man 3 stat man 3 getpwuid man -k uid | grep get man getgrgid

see ls2.c and use ls2

ls2.c cannot use cannot use specified directory as argument. Try to fix this bug.

see ls3.c and ls4.c

1. sort: store all filename in an array and qsort it.
2. The standard ls is output in columns. The solution: read the file name into an array, and then calculate the column width and number of rows.
3. ls -a: Make ls output hidden files only when accepting option -a.