NAME
        shell - A simple shell

DESCRIPTION
        This program is a simple command line shell that executes commands read from the standard input or from a file.
        These commands can be built in (listed below) or from environment path.

        It should work in the similar manner as popular shells like bash, zsh or fish. To run a command, type it into the shell and
        press Enter. All commands are terminated with newline character.

BUILT-IN COMMANDS
    cd      Change the current directory to the one specified after the command. If the directory specified does not exist
            report an error. If there is no argument, change to $HOME.
    
    clr     Clear the screen.

    ls      List the contents of a directory.

    environ List all the environment strings.

    export  Followed by a key=value pair, add new environment variables.

    echo    Followed by a string and print that string onto the screen with a newline character.

    help    Display the user manual.

    pause   Pause the operation of the shell until <CR> is pressed

    quit    Quit the shell.

I/O REDIRECTION
        Output of one command can be chained to the input of another command. The syntax is as follow:
            $ cmd1 | cmd2
        where cmd1 sends data through pipe to cmd2.

        Output of commands can be redirected from stdout to a file with a symbol:
            $ cmd > file
        In this case, the output of cmd is redirected to file, if file does not exist then the shell will create one.

        Input of commands can be from a file:
            $ cmd < file
        The command cmd takes input from file.

BACKGROUND PROCESS
        By default, when a program runs, the shell waits for it to finish before the user can perform any further action. However,
        in order to run a program in background, add '&' immediately after the command name, such as:
            $ [command name]&

        In this case, the process runs silently in background and the user can continue using the shell.

FILES
    shell.c     Main components of the shell
    util.c      Built-in functions for this shell
    shell.h     Header file with function declarations and constant definitions

AUTHOR
        Tu Tran
        Email: [email protected]