first commit

CS575_myz540_p1.cc

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+/*  
+	CS575 Operating Systems
+	Mike Zhong
+	10/2/16
+	Program 1
+*/
+// Header files needed 
+#include <stdio.h>
+#include <iostream>
+#include <vector>
+#include <cstring>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <ctype.h>
+#include <errno.h>
+#include <list>
+#include <fcntl.h>
+
+// Define constants
+#define MAXLINE 1024
+#define MAXARGS 20
+#define PROMPT "MZshell> "
+#define HISTSIZE 10 // history size
+
+using namespace std;
+
+int parseCmd(const char *cmdline, char** arglist, int* flags);
+
+int main(int argc, char *argv[])
+{
+
+	list<string> cmd_history;
+
+	while(1){
+
+		// declare local variables
+		pid_t pid;	
+		char cmd_buffer[MAXLINE];
+		char* arglist[MAXARGS];
+		char* args_passed[MAXARGS];
+		int argcount = 0;
+		int end_of_args = 0;
+		int last_arg = 0;
+		string temp_string;
+		int flags[4] = {0,0,0,0}; // flags array for signalling &, <, >, |
+		char* input = NULL; // input redirection
+		char* output = NULL; // output redirection
+		int pipefd[2];
+
+		// prompt and attemp to read in command
+		cout << "\n" << PROMPT << flush;
+		cin.getline(cmd_buffer, MAXLINE);
+		// if user enters nothing, keep prompting
+		while(cmd_buffer[0] == '\0'){
+			cout << "\n" << PROMPT << flush;
+			cin.getline(cmd_buffer, MAXLINE);
+		}
+
+		temp_string = cmd_buffer; // convert to string object for history
+
+		// cout << cmd_buffer << endl;
+
+		// add command to history, limit to 10 items
+		if(cmd_history.size() < HISTSIZE){
+			cmd_history.push_front(temp_string);
+		}
+		else{
+			cmd_history.pop_back();
+			cmd_history.push_front(temp_string);
+		} 		
+
+		// parse command
+		argcount = parseCmd(cmd_buffer, arglist, flags);
+
+		last_arg = argcount - 1;
+
+		for(int i = 0; i < argcount; ++i){
+
+			// printf("arglist[%d]: %s ", i, arglist[i]); 
+			// check input and output redirection
+			// case of main < input.txt > output.txt
+			if(!strcmp(arglist[i], "<")){
+				if(!end_of_args){
+					end_of_args = 1;
+					last_arg = i - 1;
+				}
+				input = arglist[i + 1];
+				// cout << "input redirect detected, setting flag\n";
+				flags[1] = 1;
+			}
+			else if(!strcmp(arglist[i], ">")){
+				if(!end_of_args){
+					end_of_args = 1;
+					last_arg = i - 1;
+				}
+				// cout << "output redirect detected, setting flag\n";
+				output = arglist[i + 1];
+				flags[2] = 1;
+			}
+		}
+
+		// what to do now... set all arguments beyond the redirection operators to null
+		for(int i = last_arg + 1; i < argcount; ++i){
+			arglist[i] = NULL;
+		}
+
+		// not handling weird cases yet
+		// input = strstr(arglist[0], '<');
+
+		// check exit command
+		if(!strcmp(arglist[0], "exit")){	
+			exit(1);
+		}
+		// check cd command
+		else if(!strcmp(arglist[0], "cd")){
+			if(chdir(arglist[1]) < 0){
+				cout << "Directory change failed\n";
+			}
+		}// check history command
+		else if(!strcmp(arglist[0], "history")){
+			cout << "displaying history\n";
+			for(auto iter : cmd_history){
+				cout << "command: " << iter << endl;
+			}
+		}
+		else{ // no other known commands, time to execute
+			// cout << "forking now\n";
+			pid = fork();
+
+			if(pid < 0){ // failed
+				cout << "Fork failed\n";
+			}	
+			else if(pid == 0){ // child process
+				// cout << "hello from child process\n";
+				if(flags[1]){ // input redirection	
+					// printf("About to redirect input to: %s\n", input);	
+					int fd0 = open(input, O_RDONLY);
+					if(fd0 < 0){
+						cout << "open() failed\n";
+					}
+					if(dup2(fd0, STDIN_FILENO) < 0){
+						cout << "dup2() failed\n";
+					}
+					close(fd0);
+				}
+
+				if(flags[2]){ // output redirection
+					// printf("About to redirect output to: %s\n", output);
+					int fd1 = creat(output, 0644);
+					if(fd1 < 0){
+						cout << "creat() failed\n";
+					}
+					int chk1 = dup2(fd1, STDOUT_FILENO);
+					if(dup2(fd1, STDOUT_FILENO) < 0){
+						cout << "dup2() failed\n";
+					}
+					close(fd1);
+				}
+				// cout << "bout ta execute!!!\n";
+				execvp(arglist[0], arglist);
+				cout << "Unrecognized command, execvp not successful\n";
+				exit(0);
+			}
+			else{ // parent process
+
+				// cout << "hello from parent process\n";
+				if(!flags[0]){ // if it's not a background process, wait
+					// cout << "parent gonna wait\n";
+					waitpid(-1, NULL, 0);
+				}
+
+			}
+		}
+	}
+
+
+  return 0;
+}
+
+/* 
+ * parsecmd - Parse the command line and build the argv array.
+ * Return the number of arguments.
+ */
+int parseCmd(const char *cmdline, char** arglist, int* flags) 
+{
+  static char array[MAXLINE]; /* holds local copy of command line */
+  char *buf = array;          /* ptr that traverses command line */
+  char *delim;                /* points to first space delimiter */
+  int argc;                   /* number of args */
+
+  strncpy(buf, cmdline, strlen(cmdline)+1);
+  buf[strlen(buf)] = ' ';  /* replace trailing '\n' with space */
+  while (*buf && (*buf == ' ')) /* ignore leading spaces */
+    buf++;
+
+  /* Build the arglist list */
+  argc = 0;
+  // based on delimiter " "(space), separate the commandline into arglist
+  while ((delim = strchr(buf, ' ')) && (argc < MAXARGS - 1)) {
+    arglist[argc++] = buf;
+    *delim = '\0';
+    buf = delim + 1;
+
+		// check last char of arglist[0] and entirety of arglist[1] for &
+		if(*(delim - 1) == '&'){
+			flags[0] = 1;
+			*(delim - 1) = '\0';
+		}
+
+    while (*buf && (*buf == ' ')) /* ignore spaces */
+      buf++;
+  }
+  arglist[argc] = NULL;
+  return argc;
+
+}

Makefile

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+CC = g++
+CFLAGS = -g --std=c++11
+
+main:CS575_myz540_p1.cc
+	$(CC) $(CFLAGS) -o main CS575_myz540_p1.cc

README.txt

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+/************************************************************
+Mike Zhong CS575 Program 1
+
+To compile, just use the Makefile provided by typing 'make',
+followed by './main' in the terminal. Or you can type
+'g++ -o main CS575_myz540_p1.cc' and execute using './main'
+
+I did not have time to implement all the features and would
+not consider this my best work. I could not figure out how 
+to implement pipelining but the input and output redirection
+works as long as there are spaces before and after the '<'
+or '>'. The '&' allows programs to run in the background but
+must be appended directly to the program name, like 'emacs&'.
+************************************************************/
+