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#include <assert.h>
#include <fcntl.h>
#include <limits.h>
#include <poll.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#define MAX_ARGS 20
#define IS_SPECIAL(_c) (';' == _c || '\n' == _c || '&' == _c || '|' == _c)
char *PATH = "/:/bin";
int can_open(char *f) {
int rc;
if (-1 == (rc = open(f, O_RDONLY, 0)))
return 0;
close(rc);
return 1;
}
int find_path(char *file, char *buf) {
if ('/' == *file || '.' == *file) { // Real path
if (!can_open(file)) {
return 0;
}
strcpy(buf, file);
return 1;
}
char *p = PATH;
for (;;) {
char *b = p;
for (; *p && ':' != *p; p++)
;
size_t l = p - b;
strlcpy(buf, b, l);
strcat(buf, "/");
strcat(buf, file);
if (can_open(buf)) {
return 1;
}
if (!*p)
break;
p++;
}
return 0;
}
int internal_exec(char *file, char **argv) {
char r_path[PATH_MAX];
if (!find_path(file, r_path))
return 0;
if (-1 == execv(r_path, argv)) {
perror("exec");
return 0;
}
return 1;
}
int execute_program(char *s, size_t l, int ignore_rc, int f_stdout,
int *new_out) {
if (!l)
return -1;
char c[l + 1];
memcpy(c, s, l);
c[l] = 0;
char *argv[MAX_ARGS];
int args = 0;
char *p = c;
for (size_t i = 0; i <= l; i++) {
if (' ' == c[i]) {
if (p == c + i) {
for (; ' ' == *p; p++, i++)
;
i--;
continue;
}
c[i] = '\0';
if (strlen(p) == 0)
break;
argv[args] = p;
args++;
p = c + i + 1;
} else if (i == l) {
if (strlen(p) == 0)
break;
argv[args] = p;
args++;
}
}
argv[args] = NULL;
int fd[2];
pipe(fd);
int pid = fork();
if (0 == pid) {
if (new_out)
dup2(fd[1], 1);
if (-1 != f_stdout)
dup2(f_stdout, 0);
close(fd[0]);
if (!internal_exec(argv[0], argv)) {
printf("exec failed\n");
exit(1);
}
}
close(fd[1]);
if (new_out)
*new_out = fd[0];
if (ignore_rc)
return 0;
int rc;
wait(&rc);
return rc;
}
int compute_expression(char *exp) {
char *n = exp;
int ignore_next = 0;
int rc;
int f_stdout = -1;
int new_out = f_stdout;
for (; *exp; exp++) {
if (!IS_SPECIAL(*exp)) {
continue;
}
if ('\n' == *exp)
break;
if (';' == *exp) {
if (!ignore_next) {
execute_program(n, exp - n, 0, f_stdout, NULL);
}
n = exp + 1;
continue;
}
if ('&' == *exp && '&' == *(exp + 1)) {
if (!ignore_next) {
rc = execute_program(n, exp - n, 0, f_stdout, NULL);
if (0 != rc)
ignore_next = 1;
}
n = exp + 2;
exp++;
continue;
} else if ('&' == *exp) {
if (!ignore_next) {
execute_program(n, exp - n, 1, f_stdout, NULL);
}
n = exp + 1;
continue;
}
if ('|' == *exp && '|' == *(exp + 1)) {
if (!ignore_next) {
rc = execute_program(n, exp - n, 0, f_stdout, NULL);
if (0 == rc)
ignore_next = 1;
}
n = exp + 2;
exp++;
continue;
} else if ('|' == *exp) {
if (!ignore_next) {
execute_program(n, exp - n, 1, f_stdout, &new_out);
f_stdout = new_out;
}
n = exp + 1;
continue;
}
}
if (!ignore_next)
rc = execute_program(n, exp - n, 0, f_stdout, NULL);
return rc;
}
char *get_line(void) {
char *str = malloc(1024);
char *p = str;
int rc;
for (;;) {
if (0 == (rc = read(0, p, 1))) {
continue;
}
if (0 > rc) {
perror("read");
continue;
}
if (8 == *p) {
if (p == str)
continue;
putchar(*p);
p--;
continue;
}
putchar(*p);
if ('\n' == *p) {
break;
}
p++;
}
p++;
*p = '\0';
return str;
}
int main(void) {
for (;;) {
printf("/ : ");
char *l = get_line();
compute_expression(l);
free(l);
}
return 0;
}
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