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getenv(3)                BSD Library Functions Manual                getenv(3)


NAME

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


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <stdlib.h>

     char *
     getenv(const char *name);

     int
     putenv(char *string);

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

     int
     unsetenv(const char *name);


DESCRIPTION

     These functions set, unset and fetch environment variables from the host
     environment list.  For compatibility with differing environment conven-
     tions, the given arguments name and value may be appended and prepended,
     respectively, with an equal sign ``=''.  The behavior is undefined when
     an equal sign appears at any other location in name.

     The getenv() function obtains the current value of the environment vari-
     able, name.

     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 is
     equivalent to:

           setenv(name, value, 1);

     The string pointed to by string becomes part of the environment.  A pro-
     gram should not alter or free the string, and should not use stack or
     other transient string variables as arguments to putenv().  The setenv()
     function is strongly preferred to putenv().

     The unsetenv() function deletes all instances of the variable name
     pointed to by name from the list.  Note that only the variable name
     (e.g., "NAME") should be given; "NAME=value" will not work.


RETURN VALUES

     The getenv() function returns the value of the environment variable as a
     NUL-terminated string.  If the variable name is not in the current envi-
     ronment, NULL is returned.

     The setenv(), putenv(), and unsetenv() functions return the value 0 if
     successful; otherwise the value -1 is returned and the global variable
     errno is set to indicate the error.


ERRORS

     [EINVAL]           The function unsetenv() failed because name was not
                        found in the environment list.

     [ENOMEM]           The function setenv() or putenv() failed because it
                        was unable to allocate memory for the environment.


LEGACY SYNOPSIS

     #include <stdlib.h>

     void
     unsetenv(const char *name);

     unsetenv() doesn't return a value.


COMPATIBILITY

     putenv() no longer copies its input buffer.  This often appears in crash
     logs as a crash in getenv().  Avoid passing local buffers or freeing the
     memory that is passed to putenv().  Use setenv(), which still makes an
     internal copy of its buffers.

     unsetenv() no longer parses the variable name; e.g., unsetenv ("FOO=BAR")
     no longer works.  Use unsetenv("FOO").  unsetenv() also now returns a
     status value and will set errno to EINVAL if name is not a defined envi-
     ronment variable.


SEE ALSO

     csh(1), sh(1), execve(2), compat(5), environ(7)


STANDARDS

     The getenv() function conforms to ISO/IEC 9899:1990 (``ISO C90'').


BUGS

     Successive calls to setenv() or putenv() assigning a differently sized
     value to the same name will result in a memory leak.  The FreeBSD seman-
     tics for these functions (namely, that the contents of value are copied
     and that old values remain accessible indefinitely) make this bug
     unavoidable.  Future versions may eliminate one or both of these semantic
     guarantees in order to fix the bug.


HISTORY

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

BSD                            December 11, 1993                           BSD

Mac OS X 10.9.1 - Generated Wed Jan 8 06:28:05 CST 2014