A shell is a command-line interface that executes commands and manages processes. This project implements a POSIX-compliant shell capable of interpreting shell commands, executing external programs, and running builtin commands.
Learning goals:
- Deepen understanding of C programming and low-level system interactions.
- Explore process management, memory handling, and pointer usage.
- Setting up for extending the shell into penetration testing / offensive security tools.
- Basic REPL loop (
$prompt) usingfgetsfor reading commands.
- Tokenizes input into command and arguments (
argvarray). - Supports up to 64 arguments per command.
exit– exits the shell.echo– prints arguments to stdout.type– identifies whether a command is builtin or external.pwd– prints current working directory (getcwd, dynamic allocation).cd– changes current directory, supports$HOMEand relative paths.
- Finds executables in
PATH. - Uses
fork()to create child processes. - Uses
execve()to execute commands.
gcc shell.c -o shell
./shell-
Command obfuscation and encoding
- Encode/decode commands to avoid detection.
- Support Base64 or XOR encoding for input/output.
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Enhanced file system operations
- Commands like
ls,cat,download,upload. - Recursive file search and enumeration of sensitive directories.
- Commands like
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Process management
- Spawn and manage background processes.
- Inject scripts or commands into running processes.
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Networking capabilities
- Reverse shells over TCP/UDP.
- Bind shells and port forwarding.
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In-memory execution
- Execute binaries directly in memory (Meterpreter style).
- Shellcode execution and dynamic library loading.
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Persistence and stealth
- Hidden shell sessions.
- Redirection of stdout/stderr to avoid logs.