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Can I use C system() to replace bash script?

+1 vote
45 views

I can write a C program with strings and to pass it to the system to avoid the ugly bash syntax?
My Program

#include <stdlib.h>
#include <stdio.h>

static char command_name[2040] = {0};
int main(int argc, char** argv) {

    if ( argc != 2 ) {
        fprintf(stderr, "Provide command line argument for virtual image \n");
        exit(1);
    } else {
            sprintf(command_name, "qemu-kvm -m 1024 %s -netdev user,id=user.0 -device rtl8139,netdev=user.0",
                argv[1]);

    }

    return system(command_name);
}

Any suggestions are welcome?

posted Sep 2, 2015 by Ritika

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1 Answer

+1 vote

yes you can do that.
as per the manual of system()

int system(const char *command);

You can see that, will will accept a command as string.
Just make sure your string is a valid command. If the string provided in system() is not valid then the system will return -1.

answer Sep 14, 2015 by Arshad Khan
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+4 votes

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There are two files.

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    void fun1(int i)
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/* INPUT  */    
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./a.out > output
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Please share a sample program with detail code.

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I am using for loop. In for loop there is one system call OR POSIX API (EX : read , write, fopen, fclose, open, close , pthread_create etc...)
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+4 votes

Code to write data in to file example.txt.. which is working fine

// basic file operations
#include <iostream>
#include <fstream>
using namespace std;

int main () {
  ofstream myfile;
  myfile.open ("example.txt");
  myfile << "Writing this to a file.\n";
  myfile << "Writing this to a file.\n";
  myfile << "Writing this to a file.\n";
  myfile << "Writing this to a file.\n";
  myfile << "Writing this to a file.\n";
  myfile << "Writing this to a file.\n";
  myfile.close();
  return 0;
}

File : filelimit.c below which takes input as the compiled binary of above code
In this code i am setting the file size limit of process to 10 bytes and the above code is trying to write more than 10 bytes. According to below code if a process is trying to write more than 10 bytes to file it should send the signal SIGXFSZ (see more about this here)

It is not sending here... Why??

#include <stdio.h>
#include <signal.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>

void handler(int sig)
{
    if(sig == SIGXFSZ)
        printf("Inside handler with correct signal\n");
    else
        printf("Inside handler with wrong signal\n");
}


int main(int argc, char const *argv[])
{
    pid_t pid;
    pid = fork();

    if(pid == 0)
    {
        signal(SIGXFSZ, handler);

        char command[256];
        scanf("%s", command);

        int ret;

        struct rlimit rl;
        rl.rlim_cur = 10;
        rl.rlim_max = 10;
        setrlimit (RLIMIT_FSIZE, &rl);

        char *envp[] = { NULL };
        char *argv[] = { command , NULL };
        ret = execve(command, argv, envp);

        while(1);
    }
    else
    {
        printf("%d - %d\n", getpid(), pid);
        signal(SIGXFSZ, handler);
        while(1);
    }
    return 0;
}
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