background-battery.c

#include <gtk/gtk.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/errno.h>
#include <string.h>

void on_button_clicked(GtkWidget *widget, gpointer data) {
    g_print("exit on button press\n");
    exit(0);
}

int main(int argc, char* argv) {
    daemon(1,1);// running in the background forever
    for(;;){
        FILE *fp = popen("bash check.sh", "r");
        if (fp == NULL) {
            perror("popen error");
            exit(EXIT_FAILURE);
        }

        int c;
        char percent[2] = "";
        while ((c = fgetc(fp)) != EOF) {
            char charStr[2];
            sprintf(charStr, "%c", c);
            strcat(percent, charStr);    
        }
        if (pclose(fp) == -1) {
            perror("pclose error");
        }

        int battery = atoi(percent);
        if(battery>25) {
            puts("suffient battery");
        }
        else {
            puts("charge now");
            gtk_init(&argc, &argv);
            GtkWidget *window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
            gtk_window_set_title(GTK_WINDOW(window), "battery alert");
            gtk_container_set_border_width(GTK_CONTAINER(window), 100);
            GtkWidget *button = gtk_button_new_with_label("BATTERY LOW");
            // callback function
            g_signal_connect(button, "clicked", G_CALLBACK(on_button_clicked), NULL);
            gtk_container_add(GTK_CONTAINER(window), button);
            g_signal_connect(window, "destroy", G_CALLBACK(gtk_main_quit), NULL);
            gtk_widget_show_all(window);
            gtk_main();
        }
        sleep(15);
    }
    return 0;
}