putenv(3p) — Linux manual page


PUTENV(3P)                POSIX Programmer's Manual               PUTENV(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior), or
       the interface may not be implemented on Linux.

NAME         top

       putenv — change or add a value to an environment

SYNOPSIS         top

       #include <stdlib.h>

       int putenv(char *string);

DESCRIPTION         top

       The putenv() function shall use the string argument to set
       environment variable values. The string argument should point to a
       string of the form "name=value".  The putenv() function shall make
       the value of the environment variable name equal to value by altering
       an existing variable or creating a new one. In either case, the
       string pointed to by string shall become part of the environment, so
       altering the string shall change the environment.

       The putenv() function need not be thread-safe.

RETURN VALUE         top

       Upon successful completion, putenv() shall return 0; otherwise, it
       shall return a non-zero value and set errno to indicate the error.

ERRORS         top

       The putenv() function may fail if:

       ENOMEM Insufficient memory was available.

       The following sections are informative.

EXAMPLES         top

   Changing the Value of an Environment Variable
       The following example changes the value of the HOME environment
       variable to the value /usr/home.

           #include <stdlib.h>
           static char *var = "HOME=/usr/home";
           int ret;

           ret = putenv(var);


       The putenv() function manipulates the environment pointed to by
       environ, and can be used in conjunction with getenv().

       See exec() for restrictions on changing the environment in multi-
       threaded applications.

       This routine may use malloc() to enlarge the environment.

       A potential 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.

       Although the space used by string is no longer used once a new string
       which defines name is passed to putenv(), if any thread in the
       application has used getenv() to retrieve a pointer to this variable,
       it should not be freed by calling free().  If the changed environment
       variable is one known by the system (such as the locale environment
       variables) the application should never free the buffer used by
       earlier calls to putenv() for the same variable.

       The setenv() function is preferred over this function. One reason is
       that putenv() is optional and therefore less portable. Another is
       that using putenv() can slow down environment searches, as explained
       in the RATIONALE section for getenv(3p).

RATIONALE         top

       Refer to the RATIONALE section in setenv(3p).



SEE ALSO         top

       exec(1p), free(3p), getenv(3p), malloc(3p), setenv(3p)

       The Base Definitions volume of POSIX.1‐2008, stdlib.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) In the event of any discrepancy between this version and
       the original IEEE and The Open Group Standard, the original IEEE and
       The Open Group Standard is the referee document. The original
       Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                          PUTENV(3P)

Pages that refer to this page: stdlib.h(0p)exec(3p)execl(3p)execle(3p)execlp(3p)execv(3p)execve(3p)execvp(3p)getenv(3p)setenv(3p)