Programming

void launchProg(char **args, int background){	 
	 int err = -1;
	 
	 if((pid=fork())==-1){
		 printf("Child process could not be created\n");
		 return;
	 }
	 // pid == 0 implies the following code is related to the child process
	if(pid==0){
		// We set the child to ignore SIGINT signals (we want the parent
		// process to handle them with signalHandler_int)	
		signal(SIGINT, SIG_IGN);
		
		// We set parent=<pathname>/simple-c-shell as an environment variable
		// for the child
		setenv("parent",getcwd(currentDirectory, 1024),1);	
		
		// If we launch non-existing commands we end the process
		if (execvp(args[0],args)==err){
			printf("Command not found");
			kill(getpid(),SIGTERM);
		}
	 }
	 
	 if (background == 0){
		 waitpid(pid,NULL,0);
	 }else{
		 printf("Process created with PID: %d\n",pid);
	 }	 
}
 
void fileIO(char * args[], char* inputFile, char* outputFile, int option){
	 
	int err = -1;
	
	int fileDescriptor; // between 0 and 19, describing the output or input file
	
	if((pid=fork())==-1){
		printf("Child process could not be created\n");
		return;
	}
	if(pid==0){
		// Option 0: output redirection
		if (option == 0){
			// We open (create) the file truncating it at 0, for write only
			fileDescriptor = open(outputFile, O_CREAT | O_TRUNC | O_WRONLY, 0600); 
			// We replace de standard output with the appropriate file
			dup2(fileDescriptor, STDOUT_FILENO); 
			close(fileDescriptor);
		// Option 1: input and output redirection
		}else if (option == 1){
			// We open file for read only (it's STDIN)
			fileDescriptor = open(inputFile, O_RDONLY, 0600);  
			// We replace de standard input with the appropriate file
			dup2(fileDescriptor, STDIN_FILENO);
			close(fileDescriptor);
			// Same as before for the output file
			fileDescriptor = open(outputFile, O_CREAT | O_TRUNC | O_WRONLY, 0600);
			dup2(fileDescriptor, STDOUT_FILENO);
			close(fileDescriptor);		 
		}
		 
		setenv("parent",getcwd(currentDirectory, 1024),1);
		
		if (execvp(args[0],args)==err){
			printf("err");
			kill(getpid(),SIGTERM);
		}		 
	}
	waitpid(pid,NULL,0);
}


void pipeHandler(char * args[]){
	// File descriptors
	int filedes[2]; // pos. 0 output, pos. 1 input of the pipe
	int filedes2[2];
	
	int num_cmds = 0;
	
	char *command[256];
	
	pid_t pid;
	
	int err = -1;
	int end = 0;
	
	// Variables used for the different loops
	int i = 0;
	int j = 0;
	int k = 0;
	int l = 0;
	
	// First we calculate the number of commands (they are separated
	// by '|')
	while (args[l] != NULL){
		if (strcmp(args[l],"|") == 0){
			num_cmds++;
		}
		l++;
	}
	num_cmds++;
	
	while (args[j] != NULL && end != 1){
		k = 0;
		while (strcmp(args[j],"|") != 0){
			command[k] = args[j];
			j++;	
			if (args[j] == NULL){
				end = 1;
				k++;
				break;
			}
			k++;
		}
	        command[k] = NULL;
		j++;		
		
		if (i % 2 != 0){
			pipe(filedes); // for odd i
		}else{
			pipe(filedes2); // for even i
		}
		
		pid=fork();
		
		if(pid==-1){			
			if (i != num_cmds - 1){
				if (i % 2 != 0){
					close(filedes[1]); // for odd i
				}else{
					close(filedes2[1]); // for even i
				} 
			}			
			printf("Child process could not be created\n");
			return;
		}
		if(pid==0){
			if (i == 0){
				dup2(filedes2[1], STDOUT_FILENO);
			}

			else if (i == num_cmds - 1){
				if (num_cmds % 2 != 0){ // for odd number of commands
					dup2(filedes[0],STDIN_FILENO);
				}else{ // for even number of commands
					dup2(filedes2[0],STDIN_FILENO);
				}
			}else{ // for odd i
				if (i % 2 != 0){
					dup2(filedes2[0],STDIN_FILENO); 
					dup2(filedes[1],STDOUT_FILENO);
				}else{ // for even i
					dup2(filedes[0],STDIN_FILENO); 
					dup2(filedes2[1],STDOUT_FILENO);					
				} 
			}
			
			if (execvp(command[0],command)==err){
				kill(getpid(),SIGTERM);
			}		
		}
				
		if (i == 0){
			close(filedes2[1]);
		}
		else if (i == num_cmds - 1){
			if (num_cmds % 2 != 0){					
				close(filedes[0]);
			}else{					
				close(filedes2[0]);
			}
		}else{
			if (i % 2 != 0){					
				close(filedes2[0]);
				close(filedes[1]);
			}else{					
				close(filedes[0]);
				close(filedes2[1]);
			}
		}
				
		waitpid(pid,NULL,0);
				
		i++;	
	}
}
			
int commandHandler(char * args[]){
	int i = 0;
	int j = 0;
	
	int fileDescriptor;
	int standardOut;
	
	int aux;
	int background = 0;
	
	char *args_aux[256];
	
	while ( args[j] != NULL){
		if ( (strcmp(args[j],">") == 0) || (strcmp(args[j],"<") == 0) || (strcmp(args[j],"&") == 0)){
			break;
		}
		args_aux[j] = args[j];
		j++;
	}
	
	// 'exit' command quits the shell
	if(strcmp(args[0],"exit") == 0) exit(0);
	// 'pwd' command prints the current directory
 	else if (strcmp(args[0],"pwd") == 0){
		if (args[j] != NULL){
			// If we want file output
			if ( (strcmp(args[j],">") == 0) && (args[j+1] != NULL) ){
				fileDescriptor = open(args[j+1], O_CREAT | O_TRUNC | O_WRONLY, 0600); 
				// We replace de standard output with the appropriate file
				standardOut = dup(STDOUT_FILENO);
				dup2(fileDescriptor, STDOUT_FILENO); 
				close(fileDescriptor);
				printf("%s\n", getcwd(currentDirectory, 1024));
				dup2(standardOut, STDOUT_FILENO);
			}
		}else{
			printf("%s\n", getcwd(currentDirectory, 1024));
		}
	} 
 	// 'clear' command clears the screen
	else if (strcmp(args[0],"clear") == 0) system("clear");
	// 'cd' command to change directory
	else if (strcmp(args[0],"cd") == 0) changeDirectory(args);
	// 'environ' command to list the environment variables
	else if (strcmp(args[0],"environ") == 0){
		if (args[j] != NULL){
			// If we want file output
			if ( (strcmp(args[j],">") == 0) && (args[j+1] != NULL) ){
				fileDescriptor = open(args[j+1], O_CREAT | O_TRUNC | O_WRONLY, 0600); 
				// We replace de standard output with the appropriate file
				standardOut = dup(STDOUT_FILENO);
				dup2(fileDescriptor, STDOUT_FILENO); 
				close(fileDescriptor);
				manageEnviron(args,0);
				dup2(standardOut, STDOUT_FILENO);
			}
		}else{
			manageEnviron(args,0);
		}
	}
	// 'setenv' command to set environment variables
	else if (strcmp(args[0],"setenv") == 0) manageEnviron(args,1);
	// 'unsetenv' command to undefine environment variables
	else if (strcmp(args[0],"unsetenv") == 0) manageEnviron(args,2);
	else{

		while (args[i] != NULL && background == 0){

			if (strcmp(args[i],"&") == 0){
				background = 1;

			}else if (strcmp(args[i],"|") == 0){
				pipeHandler(args);
				return 1;

			}else if (strcmp(args[i],"<") == 0){
				aux = i+1;
				if (args[aux] == NULL || args[aux+1] == NULL || args[aux+2] == NULL ){
					printf("Not enough input arguments\n");
					return -1;
				}else{
					if (strcmp(args[aux+1],">") != 0){
						printf("Usage: Expected '>' and found %s\n",args[aux+1]);
						return -2;
					}
				}
				fileIO(args_aux,args[i+1],args[i+3],1);
				return 1;
			}

			else if (strcmp(args[i],">") == 0){
				if (args[i+1] == NULL){
					printf("Not enough input arguments\n");
					return -1;
				}
				fileIO(args_aux,NULL,args[i+1],0);
				return 1;
			}
			i++;
		}

		launchProg(args_aux,background);
	}
return 1;
}