Introduction

In this assignment, you will practice using system calls to access the filesystem, navigate the directory structure, and parse file stats.

Learning Outcomes

Describe the API for different operations related to files $($Module $3$ MLO $3)$

Describe the API for different operations related to directories $($Module $3$ MLO $6)$

How to define and use structures in C$?($Module $2$ MLO $3)$

Specifications

NAME

tree $-$ recursively list files and directories

SYNOPSIS

tree $[$OPTION$]...[$DIRECTORY$]...$

DESCRIPTION

Recursively list all files found in DIRECTORYs. If no DIRECTORY is provided, the current directory is used.

By default, output is sorted alphabetically.

LISTING OPTIONS

$-$a Print hidden files. By default, tree does not print hidden files beginning with a dot $(\text{'}.\text{'})$ character.

The filesystem constructs $`.\text{'}$ and $`..\text{'}$ are never printed even with the $-$a option.

$-$d Print only directories, no files.

FILE OPTIONS

$-$p Print permissions according to the mode string format specified for $`$ls$\text{'}$ according to POSIX.

$-$u Print the username, or UID # if no username is available, of the file.

$-$g Print the group name, or GID # if no group name is available, of the file.

$-$s Print the size of each file in bytes.

SORTING OPTIONS $($default: alphabetic sorting$)$

$-$r Sort the output in reverse alphabetic order.

$-$t Sort the output by last modification time instead of alphabetically.

$-$U Do not sort. List files according to directory order.

$-$h Print this message

AUTHOR

You, again!

NOTES

Source code must compile without errors againt the c$99$ standard on os$1$ to receive ANY credit. Example:

gcc $-$std$=$c$99...$

Source code must compile without errors for FULL credit, with the following flags:

gcc $-$std$=$c$99-$Wall $-$Wextra $-$Wpedantic $-$Werror $...$

Detailed instructions

In this assignment, you will write a small library that parses files and directory structures to list files and directory contents recursively in a tree format, where each subdirectory is indented from the last. You will implement basic sorting and print the file permissions, username, group, and file size.

Example output

$$./$tree $-$pugs $/$usr$/$share$/$man$/$en

$[$drwxr$-$xr$-$x root root $66]/$usr$/$share$/$man$/$en

$[$drwxr$-$xr$-$x root root $148]$ man$2$

$[-$rw$-$r$--$r$--$ root root $2407]$ close$\mathrm{.}2.$gz

$[-$rw$-$r$--$r$--$ root root $1808]$ getdomainname$\mathrm{.}2.$gz

$[-$rw$-$r$--$r$--$ root root $7736]$ getrlimit$\mathrm{.}2.$gz

$[-$rw$-$r$--$r$--$ root root $4852]$ madvise$\mathrm{.}2.$gz

$[-$rw$-$r$--$r$--$ root root $5949]$ mount$\mathrm{.}2.$gz

$[-$rw$-$r$--$r$--$ root root $1445]$ sysinfo$\mathrm{.}2.$gz

$[-$rw$-$r$--$r$--$ root root $1962]$ umask$\mathrm{.}2.$gz

$[$drwxr$-$xr$-$x root root $158]$ man$3$

$[-$rw$-$r$--$r$--$ root root $2141]$ encrypt$\mathrm{.}3.$gz

$[-$rw$-$r$--$r$--$ root root $2004]$ fclose$\mathrm{.}3.$gz

$[-$rw$-$r$--$r$--$ root root $2143]$ fflush$\mathrm{.}3.$gz

$[-$rw$-$r$--$r$--$ root root $2214]$ lockf$\mathrm{.}3.$gz

$[-$rw$-$r$--$r$--$ root root $2700]$ rand$\mathrm{.}3.$gz

$[-$rw$-$r$--$r$--$ root root $3157]$ strtok$\mathrm{.}3.$gz

$[-$rw$-$r$--$r$--$ root root $1359]$ toupper$\mathrm{.}3.$gz

$[-$rw$-$r$--$r$--$ root root $1502]$ updwtmp$\mathrm{.}3.$gz

$[$drwxr$-$xr$-$x root root $21]$ man$4$

$[-$rw$-$r$--$r$--$ root root $10229]$ st$\mathrm{.}4.$gz

$[$drwxr$-$xr$-$x root root $23]$ man$5$

$[-$rw$-$r$--$r$--$ root root $4761]$ utmp$\mathrm{.}5.$gz

$[$drwxr$-$xr$-$x root root $64]$ man$7$

$[-$rw$-$r$--$r$--$ root root $3165]$ environ$\mathrm{.}7.$gz

$[-$rw$-$r$--$r$--$ root root $4731]$ hier$\mathrm{.}7.$gz

$[-$rw$-$r$--$r$--$ root root $4278]$ suffixes$\mathrm{.}7.$gz

Guidance

In this assignment, you will be working with two source files, one of which will produce a library $($shared object$)$ and the other which acts as a test$-$bench to model a third party using your library.

What is a shared library? It's just a collection of symbol definitions $($functions$,$ objects$)$ that are packaged into a shared object $(.$so$)$ file format. If your program is linked against a shared library, any symbols that you use, which are part of that library, will have undefined values when your program starts. A program called the loader comes along during the initialization process $($before main$()$ is called$),$ and it loads the shared library into memory, and the linker updates the table of symbols to point to the appropriate locations in that library. This is actually how all of the functions and symbols you use from the standard C library work. If your program calls printf, the libc.so file is loaded into your program's virtual memory space, and the printf symbol is resolved at runtime by the linker.

Shared libraries are really useful. For one, since they contain mostly read$-$only information $($function instructions, constants$),$ shared libraries can be$,$ well, shared. There is one copy of the shared library in memory, and every program that is using it simply has it mapped into each of their private virtual memory address spaces. From the perspective of the program, it's the only one using that library. From the perspective of the kernel, it just save a bunch of memory! It also means your program is a lot smaller, since the instructions and data for common things are actually stored already in the system, separate f