putenv

PUTENV(3)                  Linux Programmer's Manual                 PUTENV(3)

NAME
       putenv - change or add an environment variable

SYNOPSIS
       #include <stdlib.h>

       int putenv(char *string);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       putenv(): _XOPEN_SOURCE
           || /* Glibc since 2.19: */ _DEFAULT_SOURCE
           || /* Glibc versions <= 2.19: */ _SVID_SOURCE

DESCRIPTION
       The  putenv()  function  adds or changes the value of environment vari-
       ables.  The argument string is of the form name=value.   If  name  does
       not already exist in the environment, then string is added to the envi-
       ronment.  If name does exist, then the value of name in the environment
       is  changed  to value.  The string pointed to by string becomes part of
       the environment, so altering the string changes the environment.

RETURN VALUE
       The putenv() function returns zero on success, or nonzero if  an  error
       occurs.  In the event of an error, errno is set to indicate the cause.

ERRORS
       ENOMEM Insufficient space to allocate new environment.

ATTRIBUTES
       For   an   explanation   of   the  terms  used  in  this  section,  see
       attributes(7).

       +----------+---------------+---------------------+
       |Interface | Attribute     | Value               |
       +----------+---------------+---------------------+
       |putenv()  | Thread safety | MT-Unsafe const:env |
       +----------+---------------+---------------------+
CONFORMING TO
       POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

NOTES
       The putenv() function is not required to be reentrant, and the  one  in
       glibc 2.0 is not, but the glibc 2.1 version is.

       Since  version  2.1.2,  the glibc implementation conforms to SUSv2: the
       pointer string given to putenv() is used.  In particular,  this  string
       becomes  part  of  the  environment;  changing it later will change the
       environment.  (Thus, it is an error is to call putenv() with  an  auto-
       matic  variable  as the argument, then return from the calling function
       while string is still part of the environment.)   However,  glibc  ver-
       sions  2.0  to  2.1.1 differ: a copy of the string is used.  On the one
       hand this causes a memory leak, and  on  the  other  hand  it  violates
       SUSv2.

       The 4.4BSD version, like glibc 2.0, uses a copy.

       SUSv2 removes the const from the prototype, and so does glibc 2.1.3.

SEE ALSO
       clearenv(3), getenv(3), setenv(3), unsetenv(3), environ(7)

COLOPHON
       This  page  is  part of release 4.15 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       https://www.kernel.org/doc/man-pages/.

GNU                               2016-03-15                         PUTENV(3)
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