putenv(3) — Linux manual page

putenv(3)               Library Functions Manual               putenv(3)

NAME

       putenv - change or add an environment variable

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <stdlib.h>

       int putenv(char *string);

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

       putenv():
           _XOPEN_SOURCE
               || /* glibc >= 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 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.  On failure, it
       returns a nonzero value, and errno is set to indicate the error.

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 │
       └─────────────────────────┴───────────────┴─────────────────────┘

STANDARDS

       POSIX.1-2008.

HISTORY

       POSIX.1-2001, SVr2, 4.3BSD-Reno.

       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 glibc 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, from glibc 2.0 to glibc 2.1.1, it
       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.

       The 4.3BSD-Reno version, like glibc 2.0, uses a copy; this is
       fixed in all modern BSDs.

       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 the man-pages (Linux kernel and C library
       user-space interface documentation) project.  Information about
       the project can be found at 
       ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report
       for this manual page, see
       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
       This page was obtained from the tarball man-pages-6.9.1.tar.gz
       fetched from
       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
       2024-06-26.  If you discover any rendering problems in this HTML
       version of the page, or you believe there is a better or more up-
       to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to
       man-pages@man7.org

Linux man-pages 6.9.1          2024-05-02                      putenv(3)

Pages that refer to this page: clearenv(3), getenv(3), pam_putenv(3), setenv(3), proc_pid_environ(5), environ(7)

---