How to replace a char * in C? - c

Question

I am currently writing a shell for school purposes and I have the problem that if I write the command "history", the "exit" command afterwards doesn't work. If you could help me I would be very happy.
Here is my code:
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#define MAX_INPUT 256
static char cwd[100];
void myprintf(char *text) {
text != NULL ?
printf("%s#rash:%s: %s\n", getenv("USER"), getcwd(cwd, sizeof(cwd)), text) :
printf("%s#rash:%s: ", getenv("USER"), getcwd(cwd, sizeof(cwd)));
}
void errprintf(char *text) {
myprintf(NULL);
printf("Couldn't run %s\n", text);
}
static char *argv[256];
static int argc;
static int pid = 0;
FILE *fhistory;
void parseInput(char *input) {
input = strtok(input, "\n");
for (argc = 0; argc < MAX_INPUT; argc++) {
argv[argc] = NULL;
}
argc = 0;
fprintf(fhistory, "%s\n", input);
char *param = strtok(input, " ");
while (param) {
argv[argc++] = param;
param = strtok(NULL, " ");
}
}
void signalHandler(int sign) {
switch (sign) {
case SIGINT: {
if (pid != 0) {
kill(pid, SIGKILL);
pid = 0;
}
break;
}
case SIGCHLD: {
if (pid != 0) {
kill(pid, SIGKILL);
pid = 0;
}
break;
}
}
}
int programs() {
if (!strcmp(argv[0], "exit")) {
return -1;
}
if (!strcmp(argv[0], "cd")) {
chdir(argv[1] == NULL ? getenv("HOME") : argv[1]);
} else {
pid = fork();
switch (pid) {
case -1: {
myprintf("Erectile Dysfunction!");
break;
}
case 0: {
if (!strcmp(argv[0], "history")) {
system("cat .rash_history.txt");
} else {
execvp(argv[0], argv);
errprintf(argv[0]);
}
break;
}
default: {
waitpid(pid, NULL, 0);
signal(SIGCHLD, signalHandler);
return 0;
}
}
}
return 1;
}
int main(void) {
signal(SIGINT, signalHandler);
char *input = NULL;
myprintf("Welcome to rash!");
fhistory = fopen(".rash_history.txt", "a");
while (input != NULL ? strncmp(input, "exit", strlen(input)) != 0 : 1) {
myprintf(NULL);
input = (char *) malloc(sizeof(char *) * MAX_INPUT);
int j;
for (j = 0; j < MAX_INPUT; j++) {
input[j] = '\0';
}
fgets(input, MAX_INPUT, stdin);
parseInput(input);
if (*(input) != '\n') {
programs();
}
}
fclose(fhistory);
return 0;
}

Answer 1

I think here while (input != NULL ? strncmp(input, "exit", strlen(input)) != 0 : 1) {
it would be strlen("exit")

Answer 2

The "input" variable take value inside your while loop only:
fgets(input, MAX_INPUT, stdin);
parseInput(input);
The parseInput uses strtok function couple times. The strtok modifies the argument string, so it not clear what value it will contains at time you will compare it with "exit".
Try to duplicate "input" string before calling strtok. Try to add debug string at the end of loop to make clear what value is into input string.