MYSHELL General Commands Manual MYSHELL

NAME myshell - C shell with command line editing

SYNOPSIS myshell [arg ...]

DESCRIPTION myshell is a basic implementation of a UNIX C shell. It includes only a command-line editor.

Argument processing
	If the first argument to the shell is a pipe or redirect, then it is
invalid. All other arguments are processed as arguments to the
executing command.

Startup and shutdown
    myshell begins by executing the command myshell. This shell will run
indefinitely until quit is entered by the user.

Built-in commands
    Non-pipable / Non-ridirectable
    The following are descriptions of unredirectable and unpipable
    builtin functions

    cd
        Changes the current working directory of myshell. Defaults to
	staying in the same directory.

	Usage: cd [arg1] or cd

    clr
        Prints a series of newlines to clear the terminal screen.

	Usage: clr

    quit
        Exits myshell implementation.

	Usage: quit

Other
    dir
        Displays all files within a directory. Defaults to the contents
	of the current working directory.

	Usage: dir [arg1] or dir

    environ
        Displays all variables of the environment.

	Usage: environ
	
    echo
	Displays the arguments passed to the command or the file
	contents passed in.

	Usage: echo [argv] or echo or echo < filename

    help
        Displays this readme file page by page. Enter more to continue
	onto the next page.

	Usage: help	    

Redirection
    Redirects input or output file streams of a program to a file. If
no piping is used, input redirection must occur before output
redirection. If piping is used, input redirect may only be used
before the first pipe and output redirection may only be used
after the final pipe.

    Usage:
      executingProgram < infile > outfile or
      executingProgram < infile | ... | otherExecutingProgram > outfile

Commands

    <
       Redirects the input stream of a running program to the
       specified file. Therefore, the contents of the file are read
       in a running program rather than information entered through
       the terminal. If the input file does not exist, an error is
       printed.

       Usage: executingProgram < inputFile
       
    >
       Redirects the output stream of a running program to the
       specified file. Therefore, a running program prints to the
       output file rather than printing to the terminal. If the
       output does not exist, one is created. If it exists, its
       contents are cleared.

       Usage: executingProgram > outputFile
       
    >>
       Redirects the output stream of a running program to the
       specified file. Therefore, a running program prints to the
       output file rather than printing to the terminal. If the
       output does not exist, one is created. If it exists, everything
       written by the running program is appended to the output file.

       Usage: executingProgram >> outputFile

Piping
    Redirects input or output streams of a program to another program. The
final program's output defaults to the terminal.
Therefore in the usage below, prog1's output goes to prog2's input.
Prog2's output goes to prog3's input. ProgN-1's output goes to progN
and progN's output goes to the terminal.

Usage: prog1 | prog2 | prog3 | ... | progN-1 | progN 

Background Execution
    Sets the entered command to run as a background process. Therefore,
the running command will fully execute, but the shell will continue
running. This allows the user to continue executing commands while the
origional command runs and prints its contents to the terminal or
wherever specified. 

    Usage: prog1 [args] &

Environment
A list of variables storing information about the shell in a
variable=value format. For example, a users current working directory
is stored as PWD=/this/is/the/absolute/path/to/the/current/directory
Environment variables are stored in all caps. These environment
variables can be updated as the user executes commands such as "cd",
which changes the PWD variable. To print all environment variables,
enter the command "environ".

Executables
Executes an executable program if it exists according to the user's
PATH environment variable. The executable is checked for existance by
looping through the environment's PATH in colon delimineted sections
from left to right. If the executable does not exist, an error is
printed. Arguments listed to the right of the executable before any
piping or file redirection are passed to the executable as argv in
main.

For Example:
    prog arg1 arg2 arg3 < in.txt > out.txt

    executes prog passing it a 2 dimensional array of chars with
    the strings prog, arg1, arg2, arg3, and NULL respectively.