setenv

int

setenv(const char *name, const char *value, int rewrite)

#include  <stdlib.h>
#include  <string.h>

char *__findenv(const char *name, int *offset);

extern char **environ;

/*
 * setenv --
 *	Set the value of the environmental variable "name" to be
 *	"value".  If rewrite is set, replace any current value.
 */
int
setenv(const char *name, const char *value, int rewrite)
{
	static char **lastenv;			/* last value of environ */
	char *C;
	int l_value, offset;

	if (*value == '=')			/* no `=' in value */
		++value;
	l_value = strlen(value);
	if ((C = __findenv(name, &offset))) {	/* find if already exists */
		if (!rewrite)
			return (0);
		if (strlen(C) >= l_value) {	/* old larger; copy over */
			while ((*C++ = *value++))
				;
			return (0);
		}
	} else {					/* create new slot */
		size_t cnt;
		char **P;

		for (P = environ; *P != NULL; P++)
			;
		cnt = P - environ;
		P = (char **)realloc(lastenv, sizeof(char *) * (cnt + 2));
		if (!P)
			return (-1);
		if (lastenv != environ)
			memcpy(P, environ, cnt * sizeof(char *));
		lastenv = environ = P;
		offset = cnt;
		environ[cnt + 1] = NULL;
	}
	for (C = (char *)name; *C && *C != '='; ++C)
		;				/* no `=' in name */
	if (!(environ[offset] =			/* name + `=' + value */
	    malloc((size_t)((int)(C - name) + l_value + 2))))
		return (-1);
	for (C = environ[offset]; (*C = *name++) && *C != '='; ++C)
		;
	for (*C++ = '='; (*C++ = *value++); )
		;
	return (0);
}

/*
 * unsetenv(name) --
 *	Delete environmental variable "name".
 */
void
unsetenv(const char *name)
{
	char **P;
	int offset;

	while (__findenv(name, &offset))	/* if set multiple times */
		for (P = &environ[offset];; ++P)
			if (!(*P = *(P + 1)))
				break;
}