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sshell.c
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sshell.c
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#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/wait.h>
#include <stdbool.h>
#include <fcntl.h>
#include <sys/stat.h>
//declarations
int mysyscall(char *inputcmd, int* message, int* numpipe);
char** parsecmd(char *cmd, char** storedstr, int* numargs);
bool checkmultipleargs(char *cmd);
void excenoarg(char* cmd, char** rrdc);
char* removeleadingspaces(char* cmd);
void excecutecmd(char* cmd, char** args, char** rrdc);
char** checkredirection(char* cmd);
void redirection(char* filename);
char** checkpipe(char* cmd, int* numpipe);
char* removetrailingspaces(char* str, unsigned long length);
void multpipe(char** pipe, int numpipe, int curpipe, char** rdc, int* message, int* fdarray[]);
void handlearguments(char* cmd, char** rdc);
int handlespecialcmd(char** parsedcmd, int numargs);
int setavariable(char** parsedcmd);
int onepipe(char** pipe, char** rdc);
int nonforkfunc(char* cmd);
int handleparsingerror(char** pip, const int* numpipe);
void printerrormessage();
#define CMDLINE_MAX 512
#define ExitStatusDevision 256
#define MaximunArguments 16
#define lowercaseA 97
#define lowercaseZ 122
char* storedvariable[26];
enum ParsingError{
Notusedone,
Notusedsecond,
MissingCommand,
TooManyArguements,
MislocatedRed,
NoOutputFile,
CannotOpen,
InvalidVarialbeName
};
void redirection(char* filename){ // redirect the output to the given file
int fd;
fd = open(filename, O_WRONLY | O_CREAT, 0644);
dup2(fd, STDOUT_FILENO);
close(fd);
}
void excecutecmd(char* cmd, char** args, char** rrdc){ // execute a program in this process
// redirect the output if needed
if (!(strcmp(rrdc[1], ">"))){
redirection(rrdc[2]);
}
execvp(cmd, args);
fprintf(stderr, "Error: Command not found\n");
exit(1);
}
void excenoarg(char* cmd, char** rrdc){ // execute the no argument command
// set the default args for no argument cmd
char *args[] = {cmd, NULL, NULL};
excecutecmd(cmd, args, rrdc);
}
int setavariable(char** parsedcmd){
// if the variable name is valid, store the value in a global variable
if (strlen(parsedcmd[1]) != 1 || parsedcmd[1][0] > lowercaseZ || parsedcmd[1][0] < lowercaseA){
fprintf(stderr, "Error: invalid variable name\n");
return (1);
}
storedvariable[parsedcmd[1][0] - lowercaseA] = strdup(parsedcmd[2]);
return (0);
}
int handlespecialcmd(char** parsedcmd, int numargs){
for (int i = 0; i < numargs; ++i) {
if (parsedcmd[i][0] == '$') {
// if there is an argument start with '$', but the following content is not 'a'-'z', return error code
if (strlen(parsedcmd[i]) != 2 || parsedcmd[i][1] > 122 || parsedcmd[i][1] < 97){
return 1;
}
// if variable name valid, replace the variable name by the value of the variable
if (storedvariable[parsedcmd[i][1]-97] == 0){
// if the variable hasn't been set up, replace it with ""
parsedcmd[i] = "";
}else{
parsedcmd[i] = strdup(storedvariable[parsedcmd[i][1]-97]);
}
}
}
return 0;
}
void handlearguments(char* cmd, char** rdc){
int numargs = 0;
bool multargs = checkmultipleargs(cmd);
if (multargs){ // if there are some arguments
// create an array of char* to store parsed string
unsigned long init_length = strlen(cmd);
char* storedstr[init_length];
char** parsedcmd;
// store the parsed cmd in the array
parsedcmd = parsecmd(cmd, storedstr, &numargs);
// Check if there is any arguments with '$'. If any, change them into stored value.
handlespecialcmd(parsedcmd, numargs);
// set the arguments
char **args = malloc(sizeof(char*)*(numargs+1));
for (int i = 0; i < numargs; ++i) {
args[i] = parsedcmd[i];
}
args[-1] = NULL;
// execute the cmd with the arguments
excecutecmd(parsedcmd[0],args,rdc);
} else{
// execute 1 argument program
excenoarg(cmd,rdc);
}
}
void multpipe(char** pip, int numpipe, int curpipe, char** rdc, int message[], int* fdarray[]) {
// handle commands when pipe line detected
// create the pipe and fork
int fd[2];
pipe(fd);
fdarray[curpipe-2] = fd;
pid_t pid;
pid = fork();
if (pid > 0) { // parent
int status;
waitpid(pid, &status, 0);
message[curpipe-2] = status/ExitStatusDevision;
if (curpipe == numpipe) { // connect the first process to the pipe
close(fdarray[curpipe-2][1]);
dup2(fdarray[curpipe-2][0], STDIN_FILENO);
close(fdarray[curpipe-2][0]);
if (!(strcmp(rdc[1], ">"))){
handlearguments(rdc[0], rdc);
} else {
handlearguments(pip[numpipe-1], rdc);
}
}
if (curpipe < numpipe){ // connect middle processes to two pipes, one for input, one for output
dup2(fdarray[curpipe-2][0], STDIN_FILENO);
dup2(fdarray[curpipe-1][1], STDOUT_FILENO);
close(fdarray[curpipe-2][0]);
close(fdarray[curpipe-2][1]);
close(fdarray[curpipe-1][0]);
close(fdarray[curpipe-1][1]);
handlearguments(pip[curpipe-1], rdc);
}
} else if (pid == 0) {
if (curpipe > 2){ // recursion if need to fork more process
multpipe(pip, numpipe, curpipe-1, rdc, message, fdarray);
} else { // connect the last pipe to the pipe
close(fdarray[curpipe-2][0]);
dup2(fdarray[curpipe-2][1], STDOUT_FILENO);
close(fdarray[curpipe-2][1]);
handlearguments(pip[0], rdc);
}
} else {
message[numpipe-curpipe] = -1;
}
}
int onepipe(char** pipe, char** rdc){ // handle command when no pipe line detected
pid_t pid;
pid = fork();
if (pid > 0){
int status;
waitpid(pid, &status, 0);
return status/ExitStatusDevision;
} else if (pid == 0){
// handle arguments with or without file redirectioni
if (!(strcmp(rdc[1], ">"))){
handlearguments(rdc[0], rdc);
} else {
handlearguments(pipe[0], rdc);
}
} else {
return (1);
}
return 0;
}
char** parsecmd(char *cmd, char** storedstr, int* numargs){ // parse the cmd by white spaces
//source code
//https://www.codingame.com/playgrounds/14213/how-to-play-with-strings-in-c/string-split
char* str = cmd;
//set deliminator as space
char Deliminator[] = " ";
char *ptr = strtok(str, Deliminator);
//store every separated command into the array
while (ptr != NULL)
{
storedstr[*numargs] = ptr;
ptr = strtok(NULL, Deliminator);
(*numargs)++;
}
return storedstr;
}
bool checkmultipleargs(char *cmd){
// check if there are multiple arguments
// similar with parsecmd function but with different arguments
char Delimiter[] = " ";
char duplicatedcmd[strlen(cmd)];
strcpy(duplicatedcmd, cmd);
char *ptr = strtok(duplicatedcmd, Delimiter);
int i = 0;
while(ptr != NULL)
{
ptr = strtok(NULL, Delimiter);
i ++;
}
// if there are only 1 arguments, the loop will only loop once, in which case i will equal to 1
if (i == 1) return false;
else return true;
}
int nonforkfunc(char* cmd){
int numargs = 0;
bool multargs = checkmultipleargs(cmd);
unsigned long init_length = strlen(cmd);
char* storedstr[init_length];
char** parsedcmd;
// parse the cmd and store them in an array
parsedcmd = parsecmd(cmd, storedstr, &numargs);
if (multargs){
// If cmd is set, try to set it. If failed, return error code.
if (!strcmp(parsedcmd[0],"set")){
return (setavariable(parsedcmd) + 1);
} else if (!strcmp(parsedcmd[0],"cd")){
//If cmd is cd, try to cd it. If failed, return error code.
int chdirresult = chdir(parsedcmd[1]);
if (chdirresult == -1) {
fprintf(stderr, "Error: Cannot cd into directory\n");
return (2);
}
return (1);
}
} else{
// apply pwd directly if cmd is pwd
if (!strcmp(parsedcmd[0],"pwd")){
printf("%s\n", get_current_dir_name());
return (1);
} else if (!strcmp(parsedcmd[0],"set")){
// if cmd is set with no argument, return error code
fprintf(stderr, "Error: invalid variable name\n");
return (2);
}
}
return 0;
}
int handleparsingerror(char** pip, const int* numpipe){ // handle paring errors in the command
int statreturn;
struct stat stats;
char** rdc;
char** mrdc;
int numargs = 0;
// iterate through each pipe separated command
for (int i = 0; i < *numpipe; i++){
if (!(strcmp(pip[i], ""))){
return MissingCommand;
}
rdc = checkredirection(pip[i]);
numargs = 0;
// parse the chosen block of pipe and parse it into multiple arguments
char* storedstr[strlen(pip[i])];
char* dupedpip = strdup(pip[i]);
char** parsedcmd = parsecmd(dupedpip, storedstr, &numargs);
// if redirection character detected
if (!(strcmp(rdc[1], ">"))){
// if no arguments before redirection character
if (!(strcmp(rdc[0], ""))){
return MissingCommand;
}
// if the the variable after '$' is invalid, return error message
if (handlespecialcmd(parsedcmd, numargs)){
return InvalidVarialbeName;
}
// if more than 16 arguments
if (numargs > MaximunArguments){
return TooManyArguements;
// if redirection is not at the end
} else if (i != *numpipe-1){
return MislocatedRed;
// if no arguments after the redirection character
} else if (!(strcmp(rdc[2], ""))){
return NoOutputFile;
}
mrdc = checkredirection(rdc[2]);
// multiple redirections
if ((!strcmp(mrdc[1], ">")) && (!(strcmp(mrdc[0], "")))){
return NoOutputFile;
}
statreturn = stat(rdc[2], &stats);
if (statreturn != -1){
// check for writing permission
if (!(stats.st_mode & S_IWGRP)){
return CannotOpen;
}
}
} else {
// if the the variable after '$' is invalid, return error message
if (handlespecialcmd(parsedcmd, numargs)){
return InvalidVarialbeName;
}
// if more than 16 arguments
if (numargs > MaximunArguments){
return TooManyArguements;
}
}
}
return 0;
}
char** checkredirection(char* cmd) { // check if redirection character exists
// return an array of string separated by redirection character
unsigned long length = strlen(cmd);
char** rdc = malloc(length+3);
for (unsigned long i = 0; i < length; i++) {
if (cmd[i] == '>'){
rdc[0] = malloc(i+1);
strncpy(rdc[0], cmd, i);
rdc[0] = removetrailingspaces(rdc[0], i);
rdc[1] = malloc(2);
strncpy(rdc[1], cmd+i, 1);
rdc[2] = malloc(length-i);
strncpy(rdc[2], cmd+i+1, length-i-1);
rdc[2] = removeleadingspaces(rdc[2]);
rdc[1][-1] = '\0';
rdc[2][-1] = '\0';
return rdc;
}
}
rdc[1] = "";
return rdc;
}
char** checkpipe(char* cmd, int* numpipe){ // check if pipe line exists
// return am array of string separated by pipe line
unsigned long length = strlen(cmd);
char** pipe = malloc(length+4);
int count = 0;
unsigned long sum = 0;
for (unsigned long i = 0; i < length+1; i++){
if ((cmd[i] == '|') || (cmd[i] == '\0')){
for (int j = 0; j < count; j++){
sum += (strlen(pipe[j])+1);
}
pipe[count] = malloc(i+1-sum);
strncpy(pipe[count], cmd+sum, i-sum);
count++;
sum = 0;
}
}
for (int i = 0; i < count; i++) {
pipe[i] = removetrailingspaces(pipe[i], strlen(pipe[i]));
pipe[i] = removeleadingspaces(pipe[i]);
}
*numpipe = count;
return pipe;
}
char* removetrailingspaces(char* str, unsigned long length){
// Remove trailing spaces
for (unsigned long j = 0; j < length; j++){
if (str[length-j-1] != ' '){
str[length-j] = '\0';
break;
}
}
return str;
}
char* removeleadingspaces(char* cmd){
// Remove leading spaces
unsigned long numspaces = 0;
unsigned long length = strlen(cmd);
for (unsigned long i = 0; i < length+1; i++){
if (cmd[i] != ' '){
numspaces = i;
break;
}
}
cmd += numspaces;
return cmd;
}
int mysyscall(char *cmd, int* message, int* numpipe)
{
char** rdc;
char** pip;
int curpipe;
pid_t pid;
// parsing of the pipe sign from the command line
pip = checkpipe(cmd, numpipe);
curpipe = *numpipe;
int* fdarray[*numpipe-1];
// parsing of the output redirection from the command line
rdc = checkredirection(pip[*numpipe-1]);
// Check if there is any parsing error. If any, return the error value to main func.
if (handleparsingerror(pip, numpipe)) return handleparsingerror(pip, numpipe);
// execute cmd with no pipe
if (*numpipe == 1){
/* check if the cmd is special one, which doesn't need to fork
* if it is the a special one, return the return value to main func
*/
int whethernonfork;
whethernonfork = nonforkfunc(cmd);
if (whethernonfork){
return (whethernonfork -1);
}
// run the cmd with no pipe
return (onepipe(pip, rdc));
} else {
pid = fork();
if (pid > 0) {
int status;
waitpid(pid, &status, 0);
message[*numpipe-1] = status/ExitStatusDevision;
} else {
multpipe(pip, *numpipe, curpipe, rdc, message, fdarray);
}
}
free(pip);
free(rdc);
return 0;
}
void printerrormessage(int retval){
// print error message base on the return value
if (retval == MissingCommand){
fprintf(stderr, "Error: missing command\n");
} else if (retval == TooManyArguements){
fprintf(stderr, "Error: too many process arguments\n");
} else if (retval == MislocatedRed){
fprintf(stderr, "Error: mislocated output redirection\n");
} else if (retval == NoOutputFile){
fprintf(stderr, "Error: no output file\n");
} else if (retval == CannotOpen){
fprintf(stderr, "Error: cannot open output file\n");
} else if (retval == InvalidVarialbeName){
fprintf(stderr, "Error: invalid variable name\n");
}
}
int main(void)
{
char cmd[CMDLINE_MAX];
while (1) {
char *nl;
int retval;
int numpipe; //define the number of pipes
//malloc space for return message
int* message = malloc(sizeof(int)*4);
/* Print prompt */
printf("sshell@ucd$ ");
fflush(stdout);
/* Get command line */
fgets(cmd, CMDLINE_MAX, stdin);
/* Print command line if stdin is not provided by terminal */
if (!isatty(STDIN_FILENO)) {
printf("%s", cmd);
fflush(stdout);
}
/* Remove trailing newline from command line */
nl = strchr(cmd, '\n');
if (nl)
*nl = '\0';
//duplicate a cmd so that the original one will never be modified
char* dupcmd = strdup(cmd);
//remove leading and trailing spaces of the duplicated cmd
dupcmd = removeleadingspaces(dupcmd);
removetrailingspaces(dupcmd, strlen(dupcmd));
//re-print prompt if user typed in nothing or just spaces
if(!strcmp(dupcmd,"")) continue;
//exit the sshell if the cmd is exit
if (!strcmp(dupcmd, "exit")) {
//QUESTION!
fprintf(stderr, "Bye...\n");
fprintf(stderr, "+ completed 'exit' [0]\n");
break;
}
// run the cmd by the function defined myself, and get the error value
retval= mysyscall(dupcmd, message, &numpipe);
// print error message(if any) base on the return value
if (retval>=MissingCommand && retval <= InvalidVarialbeName) {
printerrormessage(retval);
continue;
}
// print complete message base on the number of pipes
if (numpipe == 1){
fprintf(stderr, "+ completed '%s' [%d]\n",cmd, retval);
}else{
fprintf(stderr, "+ completed '%s' ",cmd);
for (int i = 0; i < numpipe; ++i) {
fprintf(stderr, "[%d]", message[i]);
}
fprintf(stderr, "\n");
}
free(message);
}
return EXIT_SUCCESS;
}