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PUTENV(3P)                 POSIX Programmer's Manual                PUTENV(3P)
PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
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 vari-
       able 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 putenv() function need not 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 vari-
       able 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  envi-
       ron, 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.
       Although the space used by string is no longer used once a  new  string
       which defines name is passed to putenv(), if any thread in the applica-
       tion has used getenv() to retrieve  a  pointer  to  this  variable,  it
       should  not  be  freed  by  calling free().  If the changed environment
       variable is one known by the system (such  as  the  locale  environment
       variables) the application should never free the buffer used by earlier
       calls to putenv() for the same variable.
       The setenv() function is preferred over this function.  One  reason  is
       that  putenv() is optional and therefore less portable. Another is that
       using putenv() can slow down environment searches, as explained in  the
       RATIONALE section for getenv().
RATIONALE
       Refer to the RATIONALE section in setenv().
FUTURE DIRECTIONS
       None.
SEE ALSO
       exec, free(), getenv(), malloc(), setenv()
       The Base Definitions volume of POSIX.1-2008, <stdlib.h>
COPYRIGHT
       Portions  of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal  and  Electronics  Engineers,  Inc  and  The  Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum  1  applied.)  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.unix.org/online.html .
       Any typographical or formatting errors that appear  in  this  page  are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors,  see  https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                           PUTENV(3P)