CS4218 Shell is a command interpreter that provides a set of tools (applications): cd, pwd, ls, cat, echo, head, tail, grep, sed, find and wc. Apart from that, CS4218 Shell is a language for calling and combining these application. The language supports quoting of input data, semicolon operator for calling sequences of applications, command substitution and piping for connecting applications' inputs and outputs, IO-redirection to load and save data processed by applications from/to files. More details can be found in "Project Description.pdf" in IVLE.
CS4218 Shell requires the following versions of software:
- JDK 7
- Eclipse 4.3
- JUnit 4
Compiler compliance level must be <= 1.7
CS4218 Shell implementation has the following structure:
sg.edu.nus.comp.cs4218 is the main package. It provides basic interfaces (Application, Command, Shell) and Environment class that is used to manage current working directory. A Shell implementation works the following way: it parses and expands user's command line producing an instance of Command class. For example, parsing cat * | grep foo can yield the following structure: Pipe(Call(Cat(), ["a.txt", "b.txt"]), Call(Grep(), ["foo"])). After that, shell calls Command.evaluate method. An implementation of Command interface is responsible for calling applications in separate threads and supplying proper input/output streams. Implementations of Application interface provide application-specific functionality.
sg.edu.nus.comp.cs4218.exception contains definitions of the exceptions that can be thrown by shell and applications. ShellException is thrown when an error occurred during the execution of shell's functionality such as command line parsing. For each application, there is a separate exception that is inherited from AbstractApplicationException class.
Package sg.edu.nus.comp.cs4218.impl contains implementation classes. Implementation of applications is in sg.edu.nus.comp.cs4218.impl.app package, inplementation if shell commands is in sg.edu.nus.comp.cs4218.impl.cmd.