Part-A: Basic System Calls - gethostname() is used to get the hostname of the system.
- To get system name, I used passwd struct in <pwd.h> header file.
- strtok() is used to tokenize based on ";" and " ". - tokenizing for "&" is done manually in system.c file. - getcwd() is used to get the current working directory. - Relative path is handled properly by storing the path of the source file directory. - chdir() is used to change the current working directory. - Multiple arguments are also handled by using strtok() in a loop and storing all the locations to hop to. - Flags -l and -a and all combinations with repititions are handled. - Structures stat and dirent are used. - stat() is used to get the file information(file type and permissions). - qsort() is used to sort in alphabetical order. - Aliases ~, ., .. and - are handled appropriately. - Commands stored in an array. Log array is loaded at the start of the shell. - As array is updated, file is updated. - To purge, file is overwritten. To execute, command is retrieved from the array and executed. - Commands are tokenized based on "&" and stored in an array. - Executed using execvp(). time.h library used to check whether foreground process exceeds 2 seconds. - For background processes, they are added to process table, to store and retrieve them later. (to know the name of the process based on PID) - Completion of background process and printing the notification is done by signal handler function. - /proc directory is used to get the information of the process. - The contents of /proc/PID/stat are parsed to get the required information. - Prints absolute path of the process executable(for that section) - only two flags which are space separated may be given. That is, -fe, -de.. such cannot be given. - Again, dirent and stat structures are used. - Mentioned directory is recursively searched for the matching name, and the path is printed based on the color scheme. Part-B: Processes, Files and Misc. (Assumptions) - For this part, I have used a file named myshrc.txt to store the aliases. - They can be of the form alias command = real_command or command = real_command. Note that there must be space before and after =. - I referred to the working of bash in case of any conflict for how a given command should be executed. - Zombie processes will be shown as "Zombie" status.