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
       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.  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 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 versions 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.

       The GNU C library implementation provides a nonstandard extension.  If
       string does not include an equal sign:

           putenv("NAME");

       then the named variable is removed from the caller's environment.

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

COLOPHON
       This page is part of release 5.03 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                               2019-03-06                         PUTENV(3)