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

NAME         top

       putenv - change or add an environment variable

SYNOPSIS         top

       #include <stdlib.h>

       int putenv(char *string);

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

       putenv(): _SVID_SOURCE || _XOPEN_SOURCE

DESCRIPTION         top

       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

RETURN VALUE         top

       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

ERRORS         top

       ENOMEM Insufficient space to allocate new environment.

CONFORMING TO         top

       SVr4, POSIX.1-2001, 4.3BSD.

NOTES         top

       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         top

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

COLOPHON         top

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GNU                              2013-04-19                        PUTENV(3)