tangym27/project1

Project 1: Shell[ing] out commands.

Maia and MiSHELL (its like maya and miguel haha)

by Maia Brydon and Michelle Tang

Basic Features (from assignment):

• Reads a line at a time, parses the line to separate the command from its arguments. It then forks and execs the command. The parent process wait until the exec'd program exits and then it should read the next command.
• Runs exit and cd
• Reads and separates multiple commands on one line with ;.
• Implement simple redirection using > (redirecting stdout) and < (redirecting stdin).
• Implement simple pipes.

Additional Features:

• Compiles!
• Handles white space (in front and back as well as between arguments ls ; ps will work.

Attempted:

• Could not get double redirection (> < in the same line) to work.
• Multiple pipes.

Bugs:

Files & Function Headers:

shell.c

Handles a lot of things. It's so shellfish. 

/*======== char * trimwhite() ==========

    Header: char * trim_white(char * str)
    Inputs: char * str
    Returns: String with excess whitespace eliminated

    Takes a string and removes the excess spaces (front and back), then
    returns the string.
    ====================*/

/*======== char * command_line() ==========
    Header: char * command_line();
    Inputs: none
    Returns: String of the command lines args given

    Prints shell prompt according to user's computer,
    then takes command line arguments from stdin and
    returns them in a char array.
    ====================*/

/*======== char ** parse_args() ==========
    Header: char ** parse_args( char * line, char * limit );
    Inputs: char * line
            char * limit
    Returns: Array of strings, or tokens, separated
    based on delimiters between args

    Takes a string, separates tokens based on delimiter
    given, then returns an array of those tokens.
    ====================*/

/*======== int find_redirect() ==========
    Header: int find_redirect(char * args);
    Inputs: char * args
    Returns: Int corresponding to which special
    character is present

    Takes a string and determines whether piping or
    redirection is being requested. Returns 1
    if a '|' is present, returns 2 if a '>' is present,
    returns 3 if a '<' is present.
    ====================*/

/*======== int * redirect_pipe() ==========
    Header: int redirect_pipe(char ** args);
    Inputs: char ** args
    Returns: 0

    Given an array of strings, pipes arg 0,
    copies what is in stdout into a char array,
    pipes arg 1, copies the char array into input
    for arg 1. Returns 0.
    ====================*/

/*======== int * redirect_stdout() ==========
    Header: int redirect_input(char * line);
    Inputs: char * line
    Returns: 0

    Given a command, it will separate the string into
    two arrays, what is before and after the '>'. 
    It will then direct the output of the first array
    into the second array.
    ====================*/

/*======== int * redirect_stdin() ==========
    Header: int redirect_output(char * line);
    Inputs: char * line
    Returns: 0

    Given a command, it will separate the string into
    two arrays, what is before and after the '<'. 
    It will then run the first array from the results 
    of the second array.
    ====================*/

main.c

/*======== char * main() ==========
    Header: int main();
    Inputs: none
    Returns: 0 (if exited)

    Parses the command line args with ';' as a delimiter,
    trims whitespace, checks if redirection or piping is
    needed, checks if arg given is cd or exit, then forks
    off a child process, runs it, and returns to the parent.
    Repeats until all command line arguments have been
    addressed, then proceeds to print out the command prompt.
    ====================*/