Project 1: Shell-ing out commands

Connie Lei

Features:

• Can separate multiple commands on a line with ;
• Single redirection > and < functionality (will cause files to be overwritten like normally)
• Single pipe | functionality
• Can use cd to change directories, but becomes buggy, refer to bugs for more info
• Can use exit
• Bad commands will let user know they failed
• Prompt displayed
• Random/extra spaces are taken care of

Attempted:

The following did not end up working, but have been left in the code, commented out.

• Worked on multiple redirection in the mess that is foo.c
• Tried making mutliple pipes work, but then started to go down rabbit holes and never getting out, kept breaking

Bugs:

• After using cd to go up a directory level, some commands begin to break for some unknown reason. Using cd .. and then ls will sometimes break it. It seems to happen randomly and I've to debug this, but my head isn't working right now. Moving down a directory will give an error /usr/bin/cd: line 4: cd: systems-shell: No such file or directory but it will still sometimes move you down to the directory.
• The prompt will break depending on what machine you are using. I tested it while sshing into the school computers and also while on the the school computers and it comes out funny like. My laptop gives me alohomora:systems-shell connielei$ so that is the one I based the prompt off of. It will probably break if you have fancy path customizations or something.

Files & Function Headers:

I actually had one large file and aesthetics, but I broke most of it up for the sake of cutting it up.

aesthetics

Handles the command prompt
/*======== void prompt() ==========
Inputs:  void
Returns: void

prints out the command prompt,
is called before each user input
====================*/

parse.c

/*======== void printarr() ==========
Inputs:  char* args[]
Returns: void

prints out the commands to be executed in array format,
used for debugging
====================*/

/*======== char ** parse_args ==========
Inputs:  char *line 
Returns: Pointer to the beginning of line

Removes leading and trailing whitespace on the string line.
Terminating '\0' is placed at a new location if necessary.
====================*/

command.c

/*======== void special_exec ==========
Inputs: char ** line
Returns: void

used for `exit` and `cd`
as name suggests, for special commands
only executable by the parent
====================*/

/*======== void execute_args ==========
Inputs:  char ** line
Returns: void

forks() and executes the commands
====================*/

/*======== void exec  ==========
Inputs:  char * command
Returns: void

runs commands with `;`
wrapper function for other executes
====================*/

spoon.c

/*======== void piping ==========
Inputs:  char * s
Returns: void

single piping functionality
only function that takes in the entire command
because it is parsed differently and used for popen()
====================*/

redirect.c

/*======== void redirecting  ==========
Inputs:  int std, char ** line 
Returns: void

std tells whether `>` or `<`
cleans up command to be execvp
opens/creates a file, fd
calls helper function redirect
====================*/

/*======== void redirect  ==========
Inputs:  int std, int fd, char ** line 
Returns: void

uses dup, dup2, and executes commands
====================*/