@(#)getenv.3 6.4 (Berkeley) 03/20/87

.AT 3 getenv, setenv, unsetenv - manipulate environmental variables

 char *getenv(name)  char *name; 

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

 void unsetenv(name)  char *name; 

Getenv searches the environment list (see environ(7)) for a string of the form name=value and returns a pointer to the string value if such a string is present, and 0 (NULL) if it is not.

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, where failure is caused by an inability to allocate space for the environment.

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.

csh(1), sh(1), execve(2), environ(7)