char* nextToken(const char** expr) {
size_t len = 1;
trimSpaces(expr);
char* special = nextSpecial(expr);
if(special) {
return special;
}
const char* p = *expr;
/* First char must match [a-zA-Z_] */
if(!(isalpha(p[0]) || p[0] == '_')) {
return NULL;
}
/* Count consecutive number of chars matching [a-zA-Z0-9_] */
while(isalnum(p[len]) || p[len] == '_') {
len++;
}
char* ret = strndup(*expr, len);
*expr += len;
return ret;
}
int main(int argc, char** argv) {
if (argc == 1) {
return 0;
}
// Check input for validity.
if (!validateInput(argc - 1, &argv[1])) {
return -1;
}
// Count number of processes on the pipeline.
for (int i = 0; argv[i] != 0; ++i) {
if (!strcmp(argv[i], "|")) {
++numProcesses;
}
}
// Open files as needed for I/O redirection.
int bound = argc - 1;
for (int i = 0; i < bound; ++i) {
int erase_redirect = 0;
// Find output redirect if it exists and open the pipe.
if (!strcmp(argv[i], ">")) {
write_fd = open(argv[i+1], O_CREAT | O_WRONLY);
if (write_fd < 0) {
perror(argv[i+1]);
exit(-1);
}
dup2(write_fd, 1);
close(write_fd);
erase_redirect = 1;
}
// Find input redirect if it exists and get the file descriptor for it.
if (!strcmp(argv[i], "<")) {
read_fd = open(argv[i+1], O_RDONLY);
if (read_fd < 0) {
perror(argv[i+1]);
exit(-1);
}
erase_redirect = 1;
}
// If a redirect is detected, eliminate the arguments and continue
// processing.
if (erase_redirect) {
for (int j = i; j < bound - 1; ++j) {
argv[j] = argv[j+2];
}
argc -= 2;
bound -= 2;
erase_redirect = 0;
--i;
}
}
// Get first command to execute.
curIndex = argc - 1;
prevIndex = curIndex;
curIndex = nextSpecial(curIndex, argv);
if (curIndex == -1) curIndex = 0;
getNextCommand(curIndex + 1, prevIndex, argv);
// If there are multiple processes, enter function to execute all processes.
if (numProcesses > 1) {
executeNext(argc, argv);
}
// Otherwise, redirect stdin if needed and execute the command.
else {
if (read_fd != -1) {
dup2(read_fd, 0);
close(read_fd);
}
execvp(command[0], command);
}
freeCommand();
}
