PUTENV(3)                 (2019-03-06)                  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 environ-
          ment variables.  The argument string is of the form
          name=value.  If name does not already exist in the environ-
          ment, 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 environ-
          ment.

     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).  allbox; lb lb lb l l l.
          Interface Attribute Value T{ putenv() T}   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;

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     PUTENV(3)                 (2019-03-06)                  PUTENV(3)

          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 envi-
          ronment.

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

     COLOPHON
          This page is part of release 5.10 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/.

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