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<i>🌊</i>rash Minishell | @42Vienna

The Creative Abort Shell

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This project goes beyond merely crafting a new shell from scratch; it endeavors to emulate the Bash source code and the GNU Bash POSIX manual while incorporating principles from compiler parsing. By referencing these authoritative sources, the project aims to meticulously implement a shell interpreter. Moreover, it documents the entire journey from ground zero to the creation of a personalized shell, serving as a valuable resource for future learners seeking insights into shell development.

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Table of Contents

• Support Features
• DevOPS Spirit
  • Embrace Development Consistency with Docker
  • How to Re-use Our CI/CD Framework For Your Own Minishell
  • Basic cowork flow and git command
• Things Before the Implementation
  • Why We Need to Follow the Bash POSIX
  • How to Avoid Corner Cases Hell at Beginning
• Implementations
  • Frontend
    • Lexer
      • Support Token Types
    • Parser
      • Why We Choose Shift-Reduced as Parsing Algorithm
      • How Shift-Reduced Algorithm Works
      • Do I Really Need a AST tree or Command Table List
      • How to Design the Grammar in Your Shell
      • How to Generate Parsing Table
  • Backend
    • Executor
      • How We Design Our Subprocess Flow
      • What Is Subshell
      • What Is The Different Between Builtins and External Command
    • Redirection
  • Cross-end
    • Expander
    • Signal
      • Signal Handling
      • Exception Handling
      • Known Issue
• How to test with Valgrind

Support Features

| Category | Module | Function | Requirement | Status | |------------|-------------|------------------------|----------------------------------------------------------------------------------------------------------|--------| | Frontend | Lexer | Tokenizing | Tokenize user input into token list. | ✅ | | | | | Support PIPE \|. | ✅ | | | | | Support logical AND &&. | ✅ | | | | | Support logical OR \|\|. | ✅ | | | | | Support sequential operator ;. | 🛇 | | | | | Support left and right parentheses () for SUBSHELL. | ✅ | | | | | Support WORD representing basic words. | ✅ | | | | | Recognize ASSIGNMENT_WORD = for local variable assignments. | ✅ | | Frontend | Parser | Syntax Analysis | Analyze syntax of token list and report syntax errors based on Shift-Reduce algorithm with predefined grammar rules and then output as command table list. | ✅ | | Frontend | Expander | Brace Expansion | Perform brace expansion to generate multiple strings based on expressions enclosed in braces {}. | 🛇 | | | | Tilde Expansion | Perform tilde expansion to replace ~ with the current user's home directory path. | 🛇 | | | | Parameter Expansion | Perform parameter expansion to replace variables and special parameters (optionally enclosed in braces {}) in a string. | ✅ | | | | Command Substitution | Perform command substitution to replace command output in a string. | 🛇 | | | | Arithmetic Expansion | Perform arithmetic expansion to evaluate mathematical expressions enclosed in $(()). | 🛇 | | | | Process Substitution | Perform process substitution to use the output of a command as a file or input to another command. | 🛇 | | | | Word Splitting | Perform word splitting to split a string into separate words based on spaces, tabs, and newlines. | ✅ | | | | Wildcard Expansion | Perform filename expansion (globbing) in the current directory to generate filenames matching a specified pattern. | ✅ | | | | Quote Removal | Remove quotes from strings to interpret them as literal values. | ✅ | | Backend | Builtins | cd | Implement cd with relative and absolute paths. | ✅ | | | | echo | Implement echo with option -n. | ✅ | | | | env | Implement env with no options or arguments. | ✅ | | | | exit | Implement exit with no options. | ✅ | | | | export | Implement export with no options. | ✅ | | | | pwd | Implement pwd with no options. | ✅ | | | | unset | Implement unset with no options. | ✅ | | Backend | Redirection | IO Redirection | Redirect STDIN with input redirection by < operator. | ✅ | | | | | Redirect HEREDOC with input redirection by << operator. | ✅ | | | | | Redirect STDOUT with output redirection by > operator. | ✅ | | | | | Redirect STDOUT append with output redirection by >> operator. | ✅ | | | | Subshell Redirection | Implement redirections and pipes between subshell groups (\|). | ✅ | | | | Pipe Redirection | Redirect STDIN/STDOUT by pipe(). | ✅ | | Backend | Assignment | Local Assignment | Assign variables local to the current shell environment or for the duration of a command following the assignment. | 🛇 | | Cross-end | Signals | Signal Handling | Handle ctrl-C as SIGINT mirroring bash's behavior. | ✅ | | | | | Handle ctrl-D as EOF mirroring bash