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GETENV(3)                  Library Functions Manual                  GETENV(3)

     getenv, getenv_r, putenv, setenv, unsetenv - environment variable

     Standard C Library (libc, -lc)

     #include <stdlib.h>

     char *
     getenv(const char *name);

     getenv_r(const char *name, char *buf, size_t len);

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

     putenv(char *string);

     unsetenv(const char *name);

     These functions set, unset and fetch environment variables from the host
     environment list.  For compatibility with differing environment
     conventions, the 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

     The unsetenv() function deletes all instances of the variable name
     pointed to by name from the list.

     The functions 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-

     [EINVAL]           The name argument to 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]           The function setenv() or putenv() failed because they
                        were unable to allocate memory for the environment.

     The function getenv_r() can return the following errors:

     [ENOENT]           The variable name was not found in the environment.

     [ERANGE]           The value of the named variable is too long to fit in
                        the supplied buffer.

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

     The 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").

     The functions setenv() and unsetenv() appeared in Version 7 AT&T UNIX.
     The putenv() function appeared in 4.3BSD-Reno.

NetBSD 10.99                   October 25, 2010                   NetBSD 10.99