C-shell by the C-shore

Joshua Weiner

Shell project01 for Systems Level Programming with Mr. DW

Functionality:

• Successfully forks commands
• Displays users current directory
• Allows for changing of directory through the cd command
• Can exit the shell or any of its processes using exit
• Simple pipes work
• Redirects work using <, >
• SIGINT works
• Parses multiple commands delineated by semicolons
• Fancy text coloring because what else should I be concerned with early in the morning?
• Child processes spawned with "&" symbol

Issues / Not achieved

• Using arrow keys to maneuver among text inputted by the user
• Had one issue where in the redirect out test, the shell would not exit the process. This created a several-gigabyte sized file, and then would eat up resources when using cat on the file. Issue seems to have been resolved.
• Was not able to resolve double redirects
• For whatever reason, cd commands into directories will be executed successfully, then spawned as a child process and fail.
• Will throw errors with multiple semicolons. This function WAS working in an earlier version, yet for whatever reason it no longer works. Was unable to diagnose the issue.

Sources Used for Reference

• C Tutorial: Pipes - Rutgers University
• Using dup2 for I/O Redirection and Pipes

Functions

• static void sighandler(int signo);
  • Takes signal in the form of an integer (SIGINT in this case)
  • Exits process
• void child_process(char ** rgs);
  • Runs child process of parent
  • Waits until child process completes or fails
• void exec_args(int pipes[], int infileno, char * cmd, char ** rgs, int i, int file_descriptor);
  • Executes the arguments in array rgs
  • First tests if there is a valid command
  • Then tests if there is a valid file descriptor (if there is a piping function, for example)
• void redirect_out(char * item, int * fd);
  • Redirects output from the shell to a file
  • File name specified in item, file descriptor specified in fd
• void redirect_in(char * item, int * fd);
  • Redirects input from a file into the shell
  • File name specified in item, file descriptor specified in fd
• void piping(char * command, int pipes[], int file_descriptor, int infileno);
  • Creates and executes pipes with the file given by file_descriptor
  • Reliant on STDIN_FILENO passed by infileno
  • Writes from pipes[1] to read from pipes[0]
• void iterate_commands_semicolon(char * line, char * address_of_line, char * iter_cmd);
  • Iterates through shell commands as delineated by semicolons
  • (Used to) but does not work with multiple semicolons in a row, throws a Segmentation Fault error