Someone Please write comments to each line of code and also explain each line in comments that what is going on in code.

#include #include #include // strtok(); strcmp() #include // dup2(); execvp() #include // exit(); execvp() #include // printf(); perror() #include #include // waitpid() #include #include

// pre-processor directives #define BUFFERSIZE 256 #define PROMPT "myShell >> " #define PROMPTSIZE sizeof(PROMPT)

// function prototypes void execute_commands(char *[], int, int); // command execution controller. int arg_found(char *[], char *, int); // index of arg if found in the array myargv void bg_process(char *[], int); // execute command in background process void first_redirect_output(char *[], int); // first redirection of the standard output void second_redirect_output(char *[], int); // second redirection of the standard output void redirect_input(char *[], int); // redirection of the standard input void single_piped_command(char *[], int); // execution of multiple commands connected by single shell pipe void execute(char *[], int); // executes a single command up to four command line arguments void pwd(); // prints current working directory void change_dir(); // changes directory void ls(); // list segments

// Begin main() int main(int argc, char** argv) {

// variable declaration and initialization char *str_line = NULL; // string line ssize_t bytes_read; size_t len = 0; const char delims[1] = " "; char *token; char *myargv[BUFFERSIZE]; // stores parsed substrings int myargc; // count of the number of arguments (token) stored in the array myargv /* * shell#0 implementation * getline() read an entire line from the stream, storing the address of * the buffer containing the text into *str_line. The buffer is null terminated * and includes the newline character, if one was found. */ printf("%s", PROMPT);

while (getline(&str_line, &len, stdin) != -1) {

myargc = 0; // reset str_line[strlen(str_line)-1] = '\0';

// Parse the line and tokenize it // strtok returns pointer to the first token token = strtok(str_line, delims);

while (token != NULL) { // store array of tokens in myargv array myargv[myargc++] = token; token = strtok(NULL, delims); } // end while loop

// At this stage we have an array of tokens ready for execution // so we match the type of command for execution based on user inputs if (myargc > 0) { // there exists at least a single command to execute

// check exit condition if (strcmp(myargv[0], "exit") == 0) { exit(-1);

} else { // execute commands execute_commands(myargv, myargc, 0); } // end if-els-if

} // end if printf("%s", PROMPT);

} // end while loop return 0; } // end main()