NAME

       putenv - change or add a value to an environment

SYNOPSIS

       #include <stdlib.h>

       int putenv(char *string);

DESCRIPTION

       The  putenv()  function  shall use the string argument to set environment variable values.
       The string argument should point to a string of the form " name= value  ".   The  putenv()
       function  shall make the value of the environment variable name equal to value by altering
       an existing variable or creating a new one. In either  case,  the  string  pointed  to  by
       string  shall  become  part  of  the  environment, so altering the string shall change the
       environment. The space used by string is no longer used once a new  string  which  defines
       name is passed to putenv().

       The  putenv()  function  need  not  be  reentrant.  A  function that is not required to be
       reentrant is not required to be thread-safe.

RETURN VALUE

       Upon successful completion, putenv() shall return 0; otherwise, it shall return a non-zero
       value and set errno to indicate the error.

ERRORS

       The putenv() function may fail if:

       ENOMEM Insufficient memory was available.

       The following sections are informative.

EXAMPLES

   Changing the Value of an Environment Variable
       The  following  example  changes  the  value of the HOME environment variable to the value
       /usr/home.

              #include <stdlib.h>
              ...
              static char *var = "HOME=/usr/home";
              int ret;

              ret = putenv(var);

APPLICATION USAGE

       The putenv() function manipulates the environment pointed to by environ, and can  be  used
       in conjunction with getenv().

       See exec() , for restrictions on changing the environment in multi-threaded applications.

       This routine may use malloc() to enlarge the environment.

       A  potential  error  is  to call putenv() with an automatic variable as the argument, then
       return from the calling function while string is still part of the environment.

       The setenv() function is preferred over this function.

RATIONALE

       The standard developers noted that putenv() is the only function available to add  to  the
       environment without permitting memory leaks.

FUTURE DIRECTIONS

       None.

SEE ALSO

       exec()   ,   getenv()   ,   malloc()   ,   setenv()  ,  the  Base  Definitions  volume  of
       IEEE Std 1003.1-2001, <stdlib.h>

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1,  2003  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  by
       the  Institute  of  Electrical  and  Electronics Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .