NAME
        myshell

    SYNOPSIS
        myshell [batch file]

    DESCRIPTION
        myshell is a simplistic shell that provides the basics of what you expect
        from a shell program.  External commands are supported as well as file
        options like redirection and piping.

    INTERACTIVE MODE
        If myshell is called with no additional arguments it will run in interactive
        mode. The shell will prompt the user for command entry and then execute the
        command.  Continues until the exit built-in command is called.

    BATCH MODE
        myshell supports running commands in batches by running the shell with a
        single argument which is the name of a batch file.  The shell will parse the
        commands line by line from the batch file just as if the user had entered
        them in interactive mode.  All features of interactive mode are also
        supported in batch mode.

    BUILT-IN COMMANDS
        cd [path]
        -   cd changes the current working directory to the directory specified at
            [path]. If no argument is given cd will print the current working
            directory.

        dir [path]
        -   dir will print the names of the files in the directory specified by
            [path].  If no argument is given dir will print all the files in the
            current working directory.

        environ [var]
        -   environ will print the value of the environment variable at [var].
            If no argument is given envrion will print out all of the environment
            variables.

        clr
        -   clr will remove all the current commands from the terminal window and
            print a new prompt.

        echo [comment]
        -   echo will print [comment] to STDOUT.  If no argument is given echo will
            print nothing.

        help
        -   help will bring you to this manual.

        pause
        -   pause will halt operations of the shell until 'enter' is pressed by the
            user.

        exit
        -   The command exit will gracefully close the shell program.

    SHELL GRAMMAR
        Pipes
            [command] [args] | [second command] [args] | ...
        The shell supports arbitrarily long chains of piped commands using the '|'
        character to connect them.  When two or more commands are piped together
        the output on STDOUT from the first command is used as the input on STDIN
        of the next command in the chain.  The first command may also have input
        redirection and the last command may have output redirection.

        Input Redirection
            [command] [args] < [filename]
        Input redirection is supported using the '<' character between a command
        and a filename.  If the file is successfully opened any input expected in
        the command from STDIN will instead come from the file.

        Output Redirection
            [command] [args] > [filename]
        Output redirection is supported using the '>' character between a command
        and a filename.  If the file is successfully opened any output expected
        from the command on STDOUT will instead be written to the file. The file
        specified will be destroyed if it exists already.

        Output Append Redirection
            [command] [args] >> [filename]
        Append redirection is supported using the sequence '>>' between a command
        and a filename.  If the file already exists it will be appended to instead
        of being overwritten.  If the file is successfully opened any output
        expected from the command on STDOUT will be written to the end of the file.

        Background Execution
            [command] [args] & [command] [args] & ...
        The shell supports execution of processes in the shell background by using
        the '&' character at the end of a command vector.  Using background
        execution it is possible to invoke multiple commands in parallel by using
        the background operator at the end of each command vector.