Here is shell.c:

#define _GNU_SOURCE //this is needed to be able to use execvpe #include #include #include #include #include #include #include #include

typedef struct { char* binary_path; char* stdin; char* stdout; char* stderr; char* arguments; char* extra_environment; short use_path; short copy_environment; short niceness; short wait; unsigned int timeout; } command;

//function prototypes void print_parsed_command(command); short parse_command(command*, char*);

//global variables here

short getlinedup(FILE* fp, char** value){ char* line = NULL; size_t n = 0; //get one line int ret = getline(&line, &n, fp);

if(ret == -1){ //the file ended return 0; } //remove at the end line[strcspn(line, " ")] = '\0'; //duplicate the string and set value *value = strdup(line); free(line);

return 1; }

//parse a command_file and set a corresponding command data structure short parse_command(command* parsed_command, char* cmdfile){ FILE* fp = fopen(cmdfile, "rb"); if(!fp){ //the file does not exist return 0; }

char* value; short ret; int intvalue;

ret = getlinedup(fp,&value); if(!ret){ fclose(fp); return 0; } parsed_command->binary_path = value;

ret = getlinedup(fp,&value); if(!ret){ fclose(fp); return 0; } parsed_command->stdin = value;

ret = getlinedup(fp,&value); if(!ret){ fclose(fp); return 0; } parsed_command->stdout = value;

ret = getlinedup(fp,&value); if(!ret){ fclose(fp); return 0; } parsed_command->stderr = value;

ret = getlinedup(fp,&value); if(!ret){ fclose(fp); return 0; } parsed_command->arguments = value;

ret = getlinedup(fp,&value); if(!ret){ fclose(fp); return 0; } parsed_command->extra_environment = value;

ret = getlinedup(fp,&value); if(!ret){ fclose(fp); return 0; } intvalue = atoi(value); if(intvalue != 0 && intvalue != 1){ fclose(fp); return 0; } parsed_command->use_path = (short)intvalue;

ret = getlinedup(fp,&value); if(!ret){ fclose(fp); return 0; } intvalue = atoi(value); if(intvalue != 0 && intvalue != 1){ fclose(fp); return 0; } parsed_command->copy_environment = (short)intvalue;

ret = getlinedup(fp,&value); if(!ret){ fclose(fp); return 0; } intvalue = atoi(value); if(intvalue 19){ fclose(fp); return 0; } parsed_command->niceness = (short)intvalue;

ret = getlinedup(fp,&value); if(!ret){ fclose(fp); return 0; } intvalue = atoi(value); if(intvalue != 0 && intvalue != 1){ fclose(fp); return 0; } parsed_command->wait = (short)intvalue;

ret = getlinedup(fp,&value); if(!ret){ fclose(fp); return 0; } intvalue = atoi(value); if(intvalue timeout = (unsigned int)intvalue;

return 1; }

//useful for debugging void print_parsed_command(command parsed_command){ printf("---------- "); printf("binary_path: %s ", parsed_command.binary_path); printf("stdin: %s ", parsed_command.stdin); printf("stdout: %s ", parsed_command.stdout); printf("stderr: %s ", parsed_command.stderr); printf("arguments: %s ", parsed_command.arguments); printf("extra_environment: %s ", parsed_command.extra_environment); printf("use_path: %d ", parsed_command.use_path); printf("copy_environment: %d ", parsed_command.copy_environment); printf("niceness: %d ", parsed_command.niceness); printf("wait: %d ", parsed_command.wait); printf("timeout: %d ", parsed_command.timeout); }

void free_command(command cmd){ free(cmd.binary_path); free(cmd.stdin); free(cmd.stdout); free(cmd.stderr); free(cmd.arguments); free(cmd.extra_environment); }

int main(int argc, char *argv[], char* env[]) {

for(int ncommand=1; ncommand

//may be useful for debugging //print_parsed_command(parsed_command);

//process_command(...); /* process_command will: - get a parsed_command variable - create a child process - set file redirection, niceness, arguments, envirionment variables, ... - call a proper variant of execv - print when a child process is created and when any child process is terminated - if necessary, wait for the termination of the program */

free_command(parsed_command); }

//remember to wait for the termination of all the child processes, regardless of the value of parsed_command.wait

}

4. Write a shell script named compile.sh. This script must compile the code in printargs.c in an program called printargs, the code in printargsandenv.c in an program called printargsandenv, and the code in shell.c in an program called shell. The printargs and printargsandenv programs will be useful to test the functionality of your shell. The code I provided in shell.c constitutes a starting point you should use to write your shell