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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(): _SVID_SOURCE || _XOPEN_SOURCE

DESCRIPTION

       The  putenv()  function  adds  or  changes  the  value  of  environment
       variables.  The argument string is of the  form  name=value.   If  name
       does  not already exist in the environment, then string is added to the
       environment.  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.

ERRORS

       ENOMEM Insufficient space to allocate new environment.

CONFORMING TO

       SVr4, POSIX.1-2001, 4.3BSD

NOTES

       The putenv() function is not required to be reentrant, and the  one  in
       libc4, libc5 and glibc 2.0 is not, but the glibc 2.1 version is.

       Description  for  libc4, libc5, glibc: If the argument string is of the
       form name, and does not contain an ’=’  character,  then  the  variable
       name  is  removed  from the environment.  If putenv() has to allocate a
       new array environ,  and  the  previous  array  was  also  allocated  by
       putenv(),  then  it  will  be  freed.   In no case will the old storage
       associated to the environment variable itself be freed.

       The libc4 and libc5 and glibc 2.1.2  versions  conform  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
       automatic variable as  the  argument,  then  return  from  the  calling
       function  while  string  is  still  part of the environment.)  However,
       glibc 2.0-2.1.1 differs: a copy of the string is used.  On the one hand
       this  causes  a  memory  leak, and on the other hand it violates SUSv2.
       This has been fixed in glibc 2.1.2.

       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

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