Simulation Flow

Simulation Flow

1. Input

• Initialize
• Readline

2. Parsing

• Lexical analysis (=Tokenizing)
• Syntax analysis (=Make Parse Tree)

3. Word Expansion

• Parameter and Variable Expansions
• Word Splitting
• Pathname Expansions
• Quote Removal

4. Command Execution

• Redirection
• Builtin Commands
• Simple Command Execution

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1. Input

Intitialize

• Shell setting
• Validator

Readline

• Used by readline library.
• Accepts input up to and including the newline character ('\n').
• Checking this time EOF
• Pass the received characters to the parser as a null-terminated string, excluding newline characters ('\n').
• Add history
• How to use ?
  • brew install readline
  • Makefile env
    • RDLINE_DIR   =     $(shell brew --prefix readline)
    • READLINE     =     -L$(RDLINE_DIR)/lib/ -lreadline
    • INCS             =     -I ./include -I$(RDLINE_DIR)/include

2. Parsing

Lexical analysis (=Tokenizing)

• Types of Token

  • WORD
  • OPERATOR
    • BRACE_LEFT((), BRACE_RIGHT()), LOGICAL_AND(&&), LOGICAL_OR(||), PIPELINE(|), RDIR_IN(<), RDIR_OUT(>), RDIR_HEREDOC(<<), RDIR_APPEND(>>)

• Split by

  • blank: space, tab, (Do not include newline)
  • operator (consist of non blank metacharacters): "(", ")", "|", "||", "&&", "<", ">", "<<", ">>"

• Notes

  • Unclosed quote, Unclosed Double quote, Unpaired Bracket,Unpaired Operator -> syntax error

Syntax analysis (=Make AST Parse Tree)

3. Word Expansion

Parameter and Variable Expansions

• Positional Parameters: $N (N is digit)

• Special Parameters

  • ?: exit status of the most recent pipeline
  • *: wild card

• Environment Variables: ${VARIABLE_NAME}

Word Splitting

Pathname Expansions

Quote Removal

4. Command Execution

Redirection

Builtin Commands

Simple Command Execution

• Error case
  • No such file or directory(/contains && does not exist)
  • No such file or directory(/contains && does not exist)
  • Permission denied(Include && Exist But Permissions denied)
  • No such file or directory(/contains && Exist But No such file)
  • command not found(/none && does not exist)