Segmentation fault in c in my code. - c

Question

I am creating a simple unix shell using c. Where there are two commands: "set prompt" which changes the user prompt and "quit" which exits the program, any other commands are taken care of by the system. I have the following code but I keep getting segmentation fault. What is it that I am accessing incorrectly. Please Help.
int main(int argc, char *argv[])
{
char cmdLine[BUFSIZ];
char *cmdPrompt = "$PROMPT:";
{
if(argc!=1)
{
printf("error: Incorrect number of arguments on command line");
}
else
{
while(1) //This creates an infinite loop as 1 will never be equals 0
{
printf("%s", cmdPrompt); //Prints the current Prompt on the screen
fgets(cmdLine, sizeof(cmdLine), stdin); //puts the user input into the cmdLine array
char *token = strtok(cmdLine, " \n"); //tokenizes the user input with delimitters space or enter
if(strcasecmp(token, "QUIT")==0) //checks if the user input is "quit"
{
exit(EXIT_SUCCESS); //successfully exits program
}
else if(strcasecmp(token, "SET")==0) //checks if the first part of user input is "set"
{
token = strtok(NULL, " \n");
if(strcasecmp(token, "PROMPT")==0) //checks to see if the next part is promt
{
token = strtok(NULL, "\n");
cmdPrompt = token; //changes the user prompt
}
else
{
system(cmdLine); //all other commands taken care of by the system
}
}
}
}
}
}

Answer 1

From the manual page (man strtok in a Unix shell):
RETURN VALUE
The strtok() and strtok_r() functions return a pointer to the next token, or NULL if there are no more tokens.
Which means you need to make sure that the returned value (token) is not a NULL pointer before using it.
Also the system() call may not like it if the cmdLine variable includes a '\n' character.
Also, fgets() can return NULL on errors:
RETURN VALUE
gets() and fgets() return s on success, and NULL on error or when end of file occurs while no characters have been read.
You should be fine on that one though.