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NAME    [Toc]    [Back]

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

LIBRARY    [Toc]    [Back]

     Standard C Library (libc, -lc)

SYNOPSIS    [Toc]    [Back]

     #include <stdlib.h>

     char *
     getenv(const char *name);

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

     putenv(const char *string);

     unsetenv(const char *name);

DESCRIPTION    [Toc]    [Back]

     These functions set, unset and fetch environment variables from the host
     environment list.	For compatibility with differing environment conventions,
 the given arguments name and value may be appended and prepended,
     respectively, 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 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 unsetenv() function deletes all instances of the variable name
     pointed to by name from the list.

RETURN VALUES    [Toc]    [Back]

     The setenv() and putenv() 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    [Toc]    [Back]

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

SEE ALSO    [Toc]    [Back]

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

STANDARDS    [Toc]    [Back]

     The getenv() function conforms to ISO/IEC 9899:1990 (``ISO C89'').

BUGS    [Toc]    [Back]

     Successive calls to setenv() or putenv() assigning a differently sized
     value to the same name will result in a memory leak.  The FreeBSD semantics
 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    [Toc]    [Back]

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

FreeBSD 5.2.1		       December 11, 1993		 FreeBSD 5.2.1
[ Back ]
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