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antony-frolov committed Mar 3, 2022
1 parent 882a4d5 commit 1bad79b
Showing 1 changed file with 321 additions and 0 deletions.
321 changes: 321 additions & 0 deletions shell.c
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#include <string.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/wait.h>
#include <sys/file.h>
#include <stdlib.h>

#define MAX_COMMANDS_N 20
#define MAX_COMMAND_LINE_LEN 100


int transporter(int arg_start, int arg_end, char *argv[]) {
pid_t last_pid;
int com_ind = 1;
unsigned end_flag = 0;
int prev_pipe[2];
while (!end_flag) {
int new_arg_end = arg_start;
while (new_arg_end < arg_end) {
if (strcmp(argv[new_arg_end], "|") == 0) {
break;
}
new_arg_end += 1;
}
char *arg_vect[new_arg_end - arg_start + 1];
arg_vect[new_arg_end - arg_start] = NULL;
int i = 0;
while (arg_start != new_arg_end) {
arg_vect[i] = argv[arg_start];
i += 1;
arg_start += 1;
}
if (arg_start == arg_end) {
end_flag = 1;
} else {
arg_start += 1;
}
int cur_pipe[2];
if (!end_flag) {
pipe(cur_pipe);
}
if ((last_pid = fork()) == 0) {
if (com_ind > 1) {
// close(prev_pipe[1]);
dup2(prev_pipe[0], 0);
}
if (!end_flag) {
close(cur_pipe[0]);
dup2(cur_pipe[1], 1);
}
execvp(arg_vect[0], arg_vect);
}
if (!end_flag) {
close(cur_pipe[1]);
}
if (com_ind > 1) {
close(prev_pipe[0]);
}
prev_pipe[0] = cur_pipe[0];
prev_pipe[1] = cur_pipe[1];
com_ind += 1;
}
int status;
int last_status = 0;
pid_t pid;
while((pid = wait(&status)) != -1) {
if (pid == last_pid) {
last_status = WEXITSTATUS(status);
}
};
return last_status;
}

int change_inoutput(int arg_ind, char *argv[]) {
if (strcmp(argv[arg_ind], "<") == 0) {
arg_ind += 1;
char *file_name = argv[arg_ind];
int fd = open(file_name, O_RDONLY);
dup2(fd, 0);
arg_ind += 1;
return 1;
} else if (strcmp(argv[arg_ind], ">") == 0) {
arg_ind += 1;
char *file_name = argv[arg_ind];
int fd = open(file_name, O_WRONLY | O_CREAT | O_TRUNC);
dup2(fd, 1);
arg_ind += 1;
return 1;
} else if (strcmp(argv[arg_ind], ">>") == 0) {
arg_ind += 1;
char *file_name = argv[arg_ind];
int fd = open(file_name, O_WRONLY | O_CREAT | O_APPEND);
dup2(fd, 1);
arg_ind += 1;
return 1;
} else return 0;
}

int command(int arg_start, int arg_end, char *argv[], int executed[]) {
if (fork() == 0) {
int status;
if (strcmp(argv[arg_start], "(") == 0) {
for (int i = arg_start; i < arg_end; i++) {
free(argv[i]);
}
int success = executed[arg_start];
exit(success);
}
int arg_ind = arg_start;
if (change_inoutput(arg_ind, argv)) {
arg_ind += 2;
if (change_inoutput(arg_ind, argv)) {

arg_ind += 2;
}
status = transporter(arg_ind, arg_end, argv);
for (int i = arg_start; i < arg_end; i++) {
free(argv[i]);
}
exit(status == 0 ? 1 : 0);
} else {
int arg_ind = arg_start;
int new_arg_end = arg_end;
while (arg_ind < arg_end) {
if ((strcmp(argv[arg_ind], ">>") == 0) || (strcmp(argv[arg_ind], ">") == 0) || (strcmp(argv[arg_ind], "<") == 0)) {
new_arg_end = arg_ind;
if (change_inoutput(arg_ind, argv)) {
arg_ind += 2;
if (change_inoutput(arg_ind, argv)) {
arg_ind += 2;
}
}
break;
}
arg_ind += 1;
}
status = transporter(arg_start, new_arg_end, argv);
for (int i = arg_start; i < arg_end; i++) {
free(argv[i]);
}
exit(status == 0 ? 1 : 0);
}
}
int st;
wait(&st);
return WEXITSTATUS(st);
}

int cond_exec_command(int arg_start, int arg_end, char *argv[], int executed[]) {
int end_flag = 0, if_yes_flag = 0, if_no_flag = 0;
int new_arg_end = arg_start;
while (new_arg_end < arg_end) {
if (strcmp(argv[new_arg_end], "&&") == 0) {
if_yes_flag = 1;
break;
} else if (strcmp(argv[new_arg_end], "||") == 0) {
if_no_flag = 1;
break;
}
new_arg_end += 1;
}
if (new_arg_end == arg_end) {
end_flag = 1;
}
int success = command(arg_start, new_arg_end, argv, executed);

if (!end_flag) {
if ((success && if_yes_flag) || (!success && if_no_flag)) {
success = cond_exec_command(new_arg_end + 1, arg_end, argv, executed);
}
}
return success;

}

int shell_command(int arg_start, int arg_end, char *argv[]) {
int executed[MAX_COMMANDS_N];
int new_arg_start = arg_start;
int new_arg_end;
int end_flag = 0;
while (!end_flag) {
while (!end_flag) {
if (strcmp(argv[new_arg_start], "(") == 0) {
new_arg_start += 1;
break;
}
new_arg_start += 1;
if (new_arg_start == arg_end) {
end_flag = 1;
break;
}
}
if (end_flag) {
break;
}
new_arg_end = new_arg_start;
int opened = 1;
while ((strcmp(argv[new_arg_end], ")") != 0) || (opened != 1)) {
if (strcmp(argv[new_arg_end], "(") == 0) {
opened += 1;
}
if (strcmp(argv[new_arg_end], ")") == 0) {
opened -= 1;
}
new_arg_end += 1;
}
int st;
if (fork() == 0) {
int status = shell_command(new_arg_start, new_arg_end, argv);
exit(status);
}
wait(&st);
executed[new_arg_start - 1] = WEXITSTATUS(st);
new_arg_start = new_arg_end;
}
end_flag = 0;
int ser_flag = 0, bg_flag = 0;
new_arg_end = arg_start;
while (new_arg_end < arg_end) {
if (strcmp(argv[new_arg_end], ";") == 0) {
ser_flag = 1;
break;
} else if (strcmp(argv[new_arg_end], "&") == 0) {
bg_flag = 1;
break;
}
new_arg_end += 1;
}
if (new_arg_end + bg_flag + ser_flag == arg_end) {
end_flag = 1;
}
int success = 0;
if (bg_flag) {
// if (fork() == 0) {
// int fd[2];
// fd[0] = open("/dev/null", O_RDONLY);
// fd[1] = open("/dev/null", O_WRONLY);
// dup2(fd[0], 0);
// dup2(fd[1], 1);
// signal(SIGINT, SIG_IGN);
// cond_exec_command(arg_start, new_arg_end, argv, executed);
// exit(0);
// }
if (fork() == 0) {
if (fork() == 0) {
int fd[2];
fd[0] = open("/dev/null", O_RDONLY);
fd[1] = open("/dev/null", O_WRONLY);
dup2(fd[0], 0);
dup2(fd[1], 1);
signal(SIGINT, SIG_IGN);
int success = cond_exec_command(arg_start, new_arg_end, argv, executed);
exit(success);
} else {
exit(0);
}
} else {
wait(NULL);
}
} else {
success = cond_exec_command(arg_start, new_arg_end, argv, executed);
}
if (!end_flag) {
shell_command(new_arg_end + 1, arg_end, argv);
}
return success;
}

char **get_argv(char *command_line, char *argv[], int *n_args) {
int i = 0;
int end_flag = (i == strlen(command_line));
int arg_ind = 0;
while (!end_flag) {
while (command_line[i] == ' ') {
i += 1;
if (i == strlen(command_line)) {
end_flag = 1;
break;
}
}
if (end_flag) {
arg_ind -= 1;
break;
}
int arg_start = i;
int arg_end;
while (command_line[i] != ' ') {
i += 1;
if (i == strlen(command_line)) {
end_flag = 1;
break;
}
}
arg_end = i;
argv[arg_ind] = (char *) malloc(arg_end - arg_start + 1);
for (int j = arg_start; j < arg_end; j++) {
argv[arg_ind][j - arg_start] = command_line[j];
}
argv[arg_ind][arg_end - arg_start] = '\0';
arg_ind += 1;
}
*n_args = arg_ind;
return argv;
}

int main() {
while (1) {
char command_line[MAX_COMMAND_LINE_LEN + 1];
fgets(command_line, MAX_COMMAND_LINE_LEN, stdin);
if (strlen(command_line) != 0) {
if (command_line[strlen(command_line) - 1] == '\n') {
command_line[strlen(command_line) - 1] = '\0';
}
}
int arg_ind;
char *argv[MAX_COMMANDS_N];
get_argv(command_line, argv, &arg_ind);
shell_command(0, arg_ind, argv);
}
return 0;
}

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