myshell

• A POSIX shell implementation in C++ [Similar to bash shell]
• Can parse and execute commands.
• Currently supported shell operators:
  • Pipe |
  • I/O redirection <, >, >>
  • Background &
  • Line separator ;

Tutorial:

• You can download the myshell.out binary and run the shell using ./myshell.out command. [Or compile the source code using make]
• Then any command and shell operator can be run using this shell.
• Example screenshot: [click on the image to zoom in]

Flow:

• From the given input command, a parse tree is built.

• Then the parse tree is executed using system calls.

  Example:

  • Command: (cmd1 | cmd2 | cmd3) < myFile.txt | cmd4; cmd7 &; cmd5 | cmd6

  • Parse tree: (((((cmd1 )|((cmd2 )|(cmd3 ))) < myFile.txt)|(cmd4 ));(((cmd7 )&);((cmd5 )|(cmd6 ))))

    

  • Parse tree will be traversed in preorder manner and each operator and exec nodes will be executed accordingly.

  • Flow: [click on the image to zoom in]

    • pread: pipe read end
    • pwrite: pipe write end
    

Files:

File	Description
parsetree/Command.cpp	Interface for parse tree nodes
parsetree/...rest...	Implementation of parse tree nodes
test-programs/	Programs to test the shell operators
util/Logger.h	For logging debug messages
util/lexer.cpp	For getting tokens from input string
util/parser.cpp	For building parse tree from tokens
util/SystemCallWrapper.cpp	Adapter class containing wrappers for C sys calls
config.cpp	For storing the config
main.cpp	Contains main function

Grammar Rules:

LINE --> null
    or, BACK
    or, BACK ';' LINE

BACK --> PIPE '&'
    or, PIPE

PIPE --> EXEC '|' PIPE
    or, EXEC

EXEC --> '(' LINE ')' REDIRECTS
    or, COMMANDARGS REDIRECTS

REDIRECTS --> null
        or, '<' FILEPATH
        or, '>' FILEPATH
        or, '>>' FILEPATH 

COMMANDARGS --> {token with supported characters for word}