environment

#define _GNU_SOURCE /* To get various declarations from <stdlib.h> */
#include <stdlib.h>
#include "tlpi_hdr.h"

extern char **environ;

int main(int argc, char *argv[])
{
  int j;
  char **ep;
 

  clearenv(); /* Erase entire environment */
 

  for (j = 1; j < argc; j++)
      if (putenv(argv[j]) != 0)
          errExit("putenv: %s", argv[j]);
 

  if (setenv("GREET", "Hello world", 0) == -1)
         errExit("setenv");
 

  unsetenv("BYE");
 

  for (ep = environ; *ep != NULL; ep++)
       puts(*ep);

  exit(EXIT_SUCCESS);
}

$ ./modify_env "GREET=Guten Tag" SHELL=/bin/bash BYE=Ciao
GREET=Guten Tag
SHELL=/bin/bash
$ ./modify_env SHELL=/bin/sh BYE=byebye
SHELL=/bin/sh
GREET=Hello world

 

char *getenv(const char *name);

int putenv(char *string);

int setenv(const char *name, const char *value, int overwrite);

int unsetenv(const char *name);

#define _BSD_SOURCE /* Or: #define _SVID_SOURCE */
#include <stdlib.h>

int clearenv(void)