Programming

#include <stdlib.h>
int main(int argc, char *argv[])
{
    char *p=getenv("USER");
    if(p==NULL) return EXIT_FAILURE;
    printf("%s\n",p);
    return 0;
    
}

/* whoami.c */
#define _PROGRAM_NAME "whoami"
#include <stdlib.h>
#include <pwd.h>
#include <stdio.h>

int main(int argc, char *argv[])
{
  register struct passwd *pw;
  register uid_t uid;
  int c;
  
  uid = geteuid ();
  pw = getpwuid (uid);
  if (pw)
    {
      puts (pw->pw_name);
      exit (EXIT_SUCCESS);
    }
  fprintf (stderr,"%s: cannot find username for UID %u\n",
	   _PROGRAM_NAME, (unsigned) uid);
  exit (EXIT_FAILURE);
  
}