Various tricks with C on Linux.

#include <stdlib.h>
#include <stdio.h>
 
int main(void) {
	FILE *f;
	char buf[256];
 
	f = fopen("/etc/hosts", "r");
	if(f) {
		while(fgets(buf, sizeof(buf), f)) {
			fputs(buf, stdout);
		}
	} else {
		printf("File not found.\n");
	}
	fclose(f);
	return 0;
}

#include <stdlib.h>
#include <stdio.h>
 
int main(void) {
	FILE *f;
	char buf[256];
 
	f = fopen("hosts", "w+");
	if(f) {
		fprintf(f, "This is appended to the file.\n");
	}
	fclose(f);
	return 0;
}

struct _kern1 {
	char *File;
	int len;
	char Kyo[40];
} *kern1 = (struct _kern1 *) 0x80;
 
void kernel(const char *File, int len)
{
	FILE *f;
	char Kyo[40];
 
	if (len > 10 or len < 2)
		return;
 
	f = fopen(File, "r");
	if(!f) {
		printf ("Sorry, I cannot open: %s.\n", File);
		printf("Please check your permissions with\n"		\
			"your supervisor. The feature may not\n"	\
			"be compiled and\\or enabled in your\n"		\
			"kernel version. Or a scsi device, eg,\n"	\
			"a USB drive may not be attached.\n");
		return;
	} else {
/* Based on sample code from:
 * www.koders.com/c/fid84CFEFBF311605F963CB04E0F84A2F52A8120F33.aspx
 * Specifically the section on parsing the /proc/version.
 */
		while (feof(f) != 1) {
			fgets(Kyo, len, f);
/*
 * This function is fast, owing to this i feel. especially with gcc 
 * 4.3.2 & glibc 2.5+. it is faster than using: printf (Kyo);
 */
			fprintf (stdout, "%s", Kyo);
			fflush(stdout);
		}
	}
	fclose(f);
}

	if (argc > 1 and strncmp(argv[1], "2", BUF) == 0) {
		printf("\t\tSystem information.\n");
 
		/* This code from:
		 * http://stackoverflow.com/questions/14345937/sysinfo-returns-incorrect-value-for-freeram-even-with-mem-unit
		 */
		/* Conversion constants. */
		const long minute = 60;
		const long hour = minute * 60;
		const long day = hour * 24;
		const double megabyte = 1024 * 1024;
 
		/* Obtain system statistics. */
		struct sysinfo si;
		sysinfo (&si);
 
		/* Summarize interesting values. */
		printf ("System uptime : %ld days, %ld:%02ld:%02ld\n",
		    si.uptime / day, (si.uptime % day) / hour,
		    (si.uptime % hour) / minute, si.uptime % minute);
		printf ("Total RAM   : %5.1f MB\n", si.totalram / megabyte);
		printf ("Free RAM   : %5.1f MB\n", si.freeram / megabyte);
		printf ("Number of running processes : %d\n", si.procs);
 
                printf("This system has %d processors configured and %d processors available.\n", get_nprocs_conf(), get_nprocs());
	}