Core Utils Reimplementation – dog & elles

This project is a personal learning exercise where I reimplemented two classic Unix tools in C:

• dog → a simplified version of cat, for printing file contents.
• elles → a simplified version of ls, for listing directory contents.

The names are a playful twist: cat vs. dog and elles sounds like l and s.

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Skills Learned

• Low-level C programming with system calls
• File I/O
• Directory handling
• File metadata
• Permission bit manipulation
• Error handling with perror
• Command-line flag parsing
• Hands-on exploration of Linux internals

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Features

dog

• Reads from one or more files and writes to standard output.
• Falls back to stdin if no files are given.
• Buffer size dynamically adjusts (up to 4096 bytes).
• Prints debug info: number of bytes read/written.
• Basic error handling for missing/unreadable files.

elles

• Lists files and directories.
• Supports:
  • -a → show hidden files
  • -l → long listing format (permissions, UID, GID, timestamp, size)
• Custom permission string formatter.
• Human-readable timestamps.
• Handles multiple paths and mixed flags.
• Error handling for invalid directories.

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Limitations

• These are not full GNU coreutils replacements.
• dog includes extra debug output not present in cat.
• elles formatting differs from real ls.

The project focuses on learning system calls, directory traversal, and Unix tool design.

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Build & Run

Requirements

• C compiler
• CMake

Build

mkdir build && cd build
cmake ..
make

Usage

# dog (like cat)
./dog file1.txt file2.txt
./dog > ouput.txt

# elles (like ls)
./elles            # default listing
./elles -a         # show hidden
./elles -l         # long format
./elles -l -a /etc   # combine flags, custom path

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Example

$ echo "hello world" > hello.txt
$ ./dog hello.txt
hello world
read 12 and written 12

$ ./elles -l
hello.txt    rw-r--r-- 1000 1000 2028-02-29 18:00:00 12