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smallsh.c
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smallsh.c
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#define _POSIX_C_SOURCE 200809L
#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <err.h>
#include <errno.h>
#include <unistd.h>
#include <ctype.h>
#include <string.h>
#include <signal.h>
#include <fcntl.h>
#ifndef MAX_WORDS
#define MAX_WORDS 512
#endif
char *words[MAX_WORDS];
size_t wordsplit(char const *line);
char * expand(char const *word);
int exit_status = 0;
int bg_child_pid = 0;
int pid_list[999999];
int pid_idx = 0;
void sigint_handler(int sig) {};
sighandler_t og_sig_STP;
sighandler_t og_sig_INT;
int main(int argc, char *argv[])
{
/* SIGNALS */
struct sigaction signal_stop;
signal_stop.sa_handler = SIG_IGN;
struct sigaction signal_int;
signal_int.sa_handler = sigint_handler;
struct sigaction oldact;
if (sigaction(SIGINT, &signal_stop, &oldact) == -1) err(1, "SIGINT Err");
struct sigaction sigstop;
if (sigaction(SIGTSTP, &signal_stop, &sigstop) == -1) err(1, "SIGTSTP Err");
FILE *input = stdin;
char *input_fn = "(stdin)";
if (argc == 2) {
input_fn = argv[1];
input = fopen(input_fn, "re");
if (!input) err(1, "%s", input_fn);
} else if (argc > 2) {
errx(1, "too many arguments");
}
char *line = NULL;
size_t n = 0;
for (;;) {
start:;
//
/* TODO: Manage background processes */
/* TODO: prompt */
if (input == stdin) { /* is interactive, otherwise is file */
char *ps1_default = getenv("PS1");
if (ps1_default != NULL) fprintf(stderr, ps1_default);
sigaction(SIGINT, &signal_int, NULL);
}
ssize_t line_len = getline(&line, &n, input);
if (input == stdin) sigaction(SIGINT, &signal_stop, NULL);
if (line_len < 0){
if (feof(input)) break;
if (errno == EINTR) {
fprintf(stderr, "\n");
clearerr(input);
errno = 0;
goto start;
}
err(1, "%s", input_fn);
}
for (int i = 0; i < pid_idx; i++) {
if (pid_list[i] != -1) {
int status = NULL;
if (waitpid(pid_list[i], &status, WNOHANG | WUNTRACED) == 0) continue;
if (WIFEXITED(status)) fprintf(stderr, "Child process %d done. Exit status %d.\n", pid_list[i], WEXITSTATUS(status));
if (WIFSIGNALED(status)) fprintf(stderr, "Child process %d done. Signaled %d.\n", pid_list[i], WTERMSIG(status));
if (WIFSTOPPED(status)) {fprintf(stderr, "Child process %d stopped. Continuing.\n", pid_list[i]);
kill(pid_list[i], SIGCONT);
}
pid_list[i] = -1;
}
}
if (feof(input)) {
exit(exit_status);
}
size_t nwords = wordsplit(line);
/* exit */
if (nwords == 0) {
exit(exit_status);
}
if (!strcmp(words[0], "exit") && strcmp(words[nwords - 1], "&")) {
char *endptr = "\0";
int value = 0;
if (nwords > 1) {
value = strtol(words[1], &endptr, 10);
}
if (*endptr != '\0' || nwords > 2) {
fprintf(stderr, "Exit Error\n");
goto prompt;
}
else {
exit(value);
}
}
/* CD */
if (strcmp(words[0], "cd") == 0) {
char *temp_dir = words[1];
if (nwords == 1) {
temp_dir = getenv("HOME");
}
if (nwords > 2) {fprintf(stderr, "Too many CD arguments.\n"); // should error exit program?
goto prompt;
}
if (chdir(temp_dir) == -1 ) {
fprintf(stderr, "CD Failed.\n");
}
goto prompt;
}
int temp = -1;
int output_index = -1;
int input_index = -1;
int app_index = -1;
/* for debudding purposes */
for (size_t i = 0; i < nwords; ++i) {
//fprintf(stderr, "Word %zu: %s\n", i, words[i]);
char *exp_word = expand(words[i]);
free(words[i]);
words[i] = exp_word;
/* Input redirection */
// background operator
if (strcmp(words[i], "&") == 0) {
temp = i;
}
// open file for writing stdout
if (strcmp(words[i], ">") == 0) {
output_index = i;
int fd = open(words[i + 1], O_RDWR| O_CREAT, 0777);
if (fd == -1) fprintf (stderr, "File couldnot be found.");
truncate(words[output_index +1], 0);
close(fd);
}
// open file for reading on stdin
if (strcmp(words[i], "<") == 0) {
input_index = i;
}
// open file for appending on stdout
if (strcmp(words[i], ">>") == 0) {
app_index = i;
}
}
/* Non Built in Commands */
/* child pid = 0, parent = child pid */
int pid = fork();
if (pid < 0) {
fprintf(stderr, "Fork failed.\n");
goto prompt;
}
else if (pid == 0) { // child
if (sigaction(SIGTSTP, &sigstop, NULL) == -1) err(1, "Sig Stop Err");
if (sigaction(SIGINT, &oldact, NULL) == -1) err(1, "Sig Int Err");
words[temp] = NULL;
if (output_index >= 0) { // >
words[output_index] = NULL;
if (output_index > app_index && freopen(words[output_index + 1], "w", stdout) == NULL)
errx(errno, "> Error");
}
if (input_index > 0) { // <
words[input_index] = NULL;
if (freopen(words[input_index + 1], "r", stdin) == NULL)
errx(errno, "< Error");
}
if (app_index > 0){ // >>
words[app_index] = NULL;
if (app_index > output_index && freopen(words[app_index + 1], "a", stdout) == NULL)
errx(errno, ">> Error");
}
if (!strcmp(words[0], "exit")) {
char *endptr = "\0";
int value = 0;
if (nwords > 1) {
value = strtol(words[1], &endptr, 10);
}
if (*endptr != '\0') {
fprintf(stderr, "Exit Error\n"); // should program end here? or just error to be thrown?
return -1;
}
else {
exit(value);
}
}
execvp(words[0], words);
return errno;
}
else {
/* waiting */
if (strcmp(words[nwords -1], "&") == 0) {
bg_child_pid = pid;
pid_list[pid_idx++] = pid;
}
else {
int status = 0;
waitpid(pid, &status, WUNTRACED);
if (WIFEXITED(status)) { // exits normally
exit_status = WEXITSTATUS(status);
}
else if (WIFSIGNALED(status)) {
exit_status = WTERMSIG(status) + 128;
}
else if (WIFSTOPPED(status))
{
fprintf(stderr, "Child process %d stopped. Continuing.\n", pid);
kill(pid, SIGCONT);
bg_child_pid = pid;
pid_list[pid_idx++] = pid;
}
}
}
prompt:;
for (int i = 0; i < nwords; i++) {
free(words[i]);
words[i] = NULL;
}
}
}
char *words[MAX_WORDS] = {0};
/* Splits a string into words delimited by whitespace. Recognizes
* comments as '#' at the beginning of a word, and backslash escapes.
*
* Returns number of words parsed, and updates the words[] array
* with pointers to the words, each as an allocated string.
*/
size_t wordsplit(char const *line) {
size_t wlen = 0;
size_t wind = 0;
char const *c = line;
for (;*c && isspace(*c); ++c); /* discard leading space */
for (; *c;) {
if (wind == MAX_WORDS) break;
/* read a word */
if (*c == '#') break;
for (;*c && !isspace(*c); ++c) {
if (*c == '\\') ++c;
void *tmp = realloc(words[wind], sizeof **words * (wlen + 2));
if (!tmp) err(1, "realloc");
words[wind] = tmp;
words[wind][wlen++] = *c;
words[wind][wlen] = '\0';
}
++wind;
wlen = 0;
for (;*c && isspace(*c); ++c);
}
return wind;
}
/* Find next instance of a parameter within a word. Sets
* start and end pointers to the start and end of the parameter
* token.
*/
char
param_scan(char const *word, char const **start, char const **end)
{
static char const *prev;
if (!word) word = prev;
char ret = 0;
*start = 0;
*end = 0;
for (char const *s = word; *s && !ret; ++s) {
s = strchr(s, '$');
if (!s) break;
switch (s[1]) {
case '$':
case '!':
case '?':
ret = s[1];
*start = s;
*end = s + 2;
break;
case '{':;
char *e = strchr(s + 2, '}');
if (e) {
ret = s[1];
*start = s;
*end = e + 1;
}
break;
}
}
prev = *end;
return ret;
}
/* Simple string-builder function. Builds up a base
* string by appending supplied strings/character ranges
* to it.
*/
char *
build_str(char const *start, char const *end)
{
static size_t base_len = 0;
static char *base = 0;
if (!start) {
/* Reset; new base string, return old one */
char *ret = base;
base = NULL;
base_len = 0;
return ret;
}
/* Append [start, end) to base string
* If end is NULL, append whole start string to base string.
* Returns a newly allocated string that the caller must free.
*/
size_t n = end ? end - start : strlen(start);
size_t newsize = sizeof *base *(base_len + n + 1);
void *tmp = realloc(base, newsize);
if (!tmp) err(1, "realloc");
base = tmp;
memcpy(base + base_len, start, n);
base_len += n;
base[base_len] = '\0';
return base;
}
/* Expands all instances of $! $$ $? and ${param} in a string
* Returns a newly allocated string that the caller must free
*/
char *
expand(char const *word)
{
char const *pos = word;
char *start, *end;
char c = param_scan(pos, &start, &end);
build_str(NULL, NULL);
build_str(pos, start);
while (c) {
if (c == '!') {
char bg_pid[32];
sprintf(bg_pid, "%d", bg_child_pid);
build_str(bg_pid, NULL);
}
else if (c == '$') {
char pid[32];
sprintf(pid, "%d", getpid());
build_str(pid, NULL);
}
else if (c == '?') {
char status_arr[32];
sprintf(status_arr, "%d", exit_status);
build_str(status_arr, NULL);
}
else if (c == '{') {
char new_arr[strlen(word) - 3];
int end = 2;
while (word[end] != '}') {
new_arr[end - 2] = word[end];
++end;
}
new_arr[end - 2] = '\0';
build_str(getenv(new_arr), NULL);
}
pos = end;
c = param_scan(pos, &start, &end);
build_str(pos, start);
}
return build_str(start, NULL);
}