| GETENV(3) | Library Functions Manual | GETENV(3) | 
getenv, getenv_r,
  putenv, setenv,
  unsetenv —
#include <stdlib.h>
char *
  
  getenv(const
    char *name);
int
  
  getenv_r(const
    char *name, char
    *buf, size_t
  len);
int
  
  setenv(const
    char *name, const char
    *value, int
    overwrite);
int
  
  putenv(char
    *string);
int
  
  unsetenv(const
    char *name);
getenv() or
  getenv_r() given argument name
  may be appended with an equal sign “=”.
The getenv() function obtains the current
    value of the environment variable name. If the
    variable name is not in the current environment, a
    NULL pointer is returned.
The getenv_r() function obtains the
    current value of the environment variable name and
    copies it to buf. If name is not
    in the current environment, or the string length of the value of
    name is longer than len
    characters, then -1 is returned and errno is set to
    indicate the error.
The setenv() function inserts or resets
    the environment variable name in the current
    environment list. If the variable name does not exist
    in the list, it is inserted with the given value. If
    the variable does exist, the argument overwrite is
    tested; if overwrite is zero, the variable is not
    reset, otherwise it is reset to the given value.
The putenv() function takes an argument of
    the form “name=value” and it will set the environment variable
    “name” equal to “value” by altering an existing
    entry, or creating a new one if an existing one does not exist. The actual
    string argument passed to putenv() will become part
    of the environment. If one changes the string, the environment will also
    change.
The unsetenv() function deletes all
    instances of the variable name pointed to by name from
    the list.
getenv_r(),
  setenv(), putenv(), and
  unsetenv() return zero if successful; otherwise the
  global variable errno is set to indicate the error and a
  -1 is returned.
If getenv() is successful, the string
    returned should be considered read-only.
EINVAL]setenv() or unsetenv() is
      a null pointer, points to an empty string, or points to a string
      containing an “=” character. The
      value argument to setenv()
      is a null pointer. The string argument to
      putenv() is a null pointer, or points to a string
      that either starts with a “=”
      character or does not contain one at all.ENOMEM]setenv() or
      putenv() failed because they were unable to
      allocate memory for the environment.The function getenv_r() can return the
    following errors:
getenv() function conforms to ANSI
  X3.159-1989 (“ANSI C89”). The
  putenv() function conforms to X/Open
  Portability Guide Issue 4 (“XPG4”). The
  unsetenv() function conforms to IEEE
  Std 1003.1-2001 (“POSIX.1”).
setenv() and
  unsetenv() appeared in
  Version 7 AT&T UNIX. The
  putenv() function appeared in
  4.3BSD-Reno.
| October 25, 2010 | NetBSD 10.0 |