minishell

A Bash-like command-line shell, built from scratch in C.

Custom lexer & parser · pipelines · redirections · heredocs · builtins · signal handling

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Overview

minishell is an interactive reimplementation of Bash, written entirely from scratch — including its own libc (libft). It reads a line of input, validates and parses it into a pipeline of commands through a hand-written lexer/parser, expands variables and quotes, then executes the pipeline via fork/execve, wiring up pipes and redirections along the way. Builtins run in-process; everything else is resolved against PATH and run as a child process. The shell tracks $?, supports command history, and handles Ctrl-C / Ctrl-\ / Ctrl-Z the way an interactive Bash session does.

Feature set

Area	Feature	Status
Parsing	Pipelines (|) of arbitrary length	✓
Parsing	Redirections <, >, >>, heredoc <<	✓
Parsing	Single & double quotes, with correct expansion rules	✓
Parsing	$VAR and $? expansion	✓
Parsing	~ expansion to $HOME	✓
Parsing	Syntax/semantic validation (unbalanced quotes, bad pipes, ambiguous redirects)	✓
Execution	fork/execve external commands	✓
Execution	PATH resolution — absolute, relative, ~, PATH-searched	✓
Execution	Exit status propagation ($?, 126/127)	✓
Execution	Multi-stage pipelines with correct fd wiring	✓
Builtins	cd, echo -n, pwd, export, unset, env, exit	✓
Signals	Ctrl-C, Ctrl-\, Ctrl-Z — matches Bash's interactive behavior	✓
Logic	&& / || operators	✗
Logic	() subshells	✗
Expansion	Wildcard / glob expansion	✗
Jobs	Job control (background jobs, suspend/resume)	✗

Detailed prompt

Building with make detailed swaps the plain $> prompt for one showing the current directory and the exit status of the last command — a green check on success, a red cross on failure:

Getting started

Requirements: a C compiler, make, GNU Readline dev headers (libreadline-dev on Debian/Ubuntu), and git.

git clone --recurse-submodules <repo-url>
cd minishell
make
./minishell

Cloned without --recurse-submodules? Run git submodule update --init --recursive before make.

Other targets: make clean · make fclean · make re · make detailed (see Detailed prompt).

In action

Verified against a built ./minishell:

$> echo "quoted $HOME end"
quoted /home/tiagoliv end

$> ls | grep m | wc -l
1

$> cat << EOF
> heredoc line one
> heredoc line two
> EOF
heredoc line one
heredoc line two

$> echo line1 > out.txt && echo line2 >> out.txt && cat < out.txt
line1
line2

$> ls does-not-exist
ls: cannot access 'does-not-exist': No such file or directory
$> echo $?
2

Architecture

src/
├── main.c, mini.c        REPL loop; shell state via the mini() singleton accessor
├── input.c                readline() wrapper for prompt input
├── signal_handle.c        SIGINT / SIGQUIT / SIGTSTP handlers
├── path.c, path_utils.c   PATH resolution (absolute / relative / ~ / PATH search)
├── pl/                    lexer & parser — builds the t_command / t_redir linked lists
├── ex/                    execution engine — fork/execve, pipes, redirections, heredocs
└── b-ins/                 builtins: cd, echo, pwd, export, unset, env, exit

libft/                     git submodule — hand-rolled libc, ft_printf, get_next_line

Each parsed line becomes a linked list of t_command nodes (one per pipeline stage), each with its own arguments and a linked list of t_redir nodes. Shell-wide state lives in a single t_mini struct reached everywhere through the mini() accessor, rather than being threaded through function calls.

Testing

.valgrindrc / leak.supp support leak-checking under valgrind. test_files/ holds sample input scripts for exercising parsing and error paths, e.g. ./minishell < test_files/simple.txt.

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A 42 School project by tiagoliv