Stop some commands used in the system() function - c

Question

I have a problem with system() function.
I need to implement a simple bash, one of the modules of the my project is to permit user types some bash command to execute it.
Above what i'm doing actually:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// similar to gets
int reads(char* str)
{
#ifndef WIN32
fflush(stdout);
strcpy(str,GetServiceLine());
#else
gets(str);
#endif
return 1;
}
int main(void) {
char str[100];
while(strcmp(str, "exit")) {
printf("\nNote: type \"exit\" to return menu\n");
printf("MyBash$ ");
reads(str);
system(str);
}
return 0;
}
My problem is with commands like ping.
When i run this code on my PC and i try execute ping command for a legal IP it works fine, i can stop the ping process using CTRL+C, but when i run it on my target on the same way i can't use CTRL+C and my process keep always at system() call.
Does somebody can help me?
Note: i read this post about how to use CTRL+C to break a system function. I tried the suggestion but didn't work.
Thanks.

Answer 1

Since you hadn't tried it yet I'll throw it up here as a suggestion. You can always install a signal handler to catch signals that you are interested in.
Here's a quick example using (mostly) your code which demonstrates how it's done:
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void intHandler(int dummy)
{
exit(1); // Do whatever you want here to handle it...
}
int main(void)
{
char str[100];
signal(SIGINT, intHandler);
signal(SIGKILL, intHandler);
while(strcmp(str, "exit")) {
printf("\nNote: type \"exit\" to return menu\n");
printf("MyBash$ ");
gets(str);
system(str);
}
return 0;
}
I can catch a ctrl+C using this, but I'm not sure if it's what you're looking for.

Answer 2

After the comments above i just thought of explaining why exactly you can't control this in a graceful manner (some hacks are suggested in comments though).
system command is going to behave exactly if you forked a child process and then called exec on the child for executing the binary passed to exec as an argument.
The system() function shall ignore the SIGINT and SIGQUIT signals, and shall block the SIGCHLD signal, while waiting for the command to terminate. If this might cause the application to miss a signal that would have killed it, then the application should examine the return value from system() and take whatever action is appropriate.
Remember, this is very much OS specific behavior and there is no standard as such.
system() function call in Linux
Internally ping utility would run on icmp and waits until a response is received from the other node.
You might write a signal handler as suggested in another answer and call a killpid() but it would be blocked until the call to system() returns. This is stated in the specs of the function. So you might be able to terminate but only AFTER the call has returned. :)

Answer 3

Below the code used to fix my problem. I don't know if is the better solution, but solved my problem in this case.
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// similar to gets
int reads(char* str)
{
#ifndef WIN32
fflush(stdout);
strcpy(str,GetServiceLine());
#else
gets(str);
#endif
return 1;
}
void getCommandName(char input[], char output[])
{
int count=0;
while (input[count] != NULL && input[count] != ' ' && input[count] != '\0') {
output[count] = input[count];
count++;
}
}
int killLastCommand(int pid)
{
char commandKill[30];
memset(commandKill, 0, 30);
sprintf(commandKill, "kill -9 %d", pid);
return(!system(commandKill));
}
int main(void) {
FILE *fp; //Will be used with popen()
char str[100];
char lastCommandName[50];
char pidofCommand[50];
char strLastPIDCommand[10];
int lastPIDCommand=0;
memset (str, 0, 100);
while(strcmp(str, "exit")) {
if (lastPIDCommand == 0) {
memset (lastCommandName, 0, 50); //Clean lastCommandName array
memset (pidofCommand, 0, 50); //Clean pidofCommand array
memset (strLastPIDCommand, 0, 10); //Clean strLastPIDCommand array
printf("\n\nNote: type \"exit\" to return menu\n");
printf("MyBash$ ");
reads(str);
if (strcmp(str, "exit")) {
sprintf(str, "%s &", str);
}
getCommandName(str, lastCommandName);
system(str);
sleep(1); //Sleep to guarantee than command will end
sprintf(pidofCommand, "pidof %s", lastCommandName);
//Saving PID
fp = popen(pidofCommand, "r");
if (fp) {
fgets(strLastPIDCommand, 10, fp);
lastPIDCommand = atoi(strLastPIDCommand);
} else {
//Handle error
}
pclose(fp);
printf("commandName = %s\r\n", lastCommandName);
printf("pid = %d\r\n", lastPIDCommand);
} else {
printf("\n\nYou have a command running, press 'kill' to stop it before to type another command\n");
printf("EITVBash$ \n\n");
reads(str);
// if (str[0] == 0x03) { //CTRL+C hexa code
if (!strcmp(str, "kill")) {
if (killLastCommand(lastPIDCommand)) {
lastPIDCommand = 0;
}
}
}
}
return 0;
}
My implementation probably isn't clean, but i don't have much experience with c.
Thanks everybody.