#include <stdlib.h>

char *
getenv(const char *name);

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

putenv(const char *string);

void
unsetenv(const char *name);

Setenv searches the environment list as getenv does; if the string name is not found, a string of the form name=value is added to the environment. If it is found, and overwrite is non-zero, its value is changed to value . Setenv returns 0 on success and -1 on failure, setting the external variable errno .

Putenv takes an argument of the form ``name=value'' and is the equivalent of:

Unsetenv removes all occurrences of the string name from the environment. There is no library provision for completely removing the current environment. It is suggested that the following code be used to do so.

static char *envinit[1];
extern char **environ;
environ = envinit;

All of these routines permit, but do not require, a trailing equals (``='') sign on name or a leading equals sign on value .

[ENOMEM] Setenv or putenv failed because they were unable to allocate memory for the environment.