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

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

       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.1‐2017, stdlib.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  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.opengroup.org/unix/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               2017                        PUTENV(3P)

Pages that refer to this page: stdlib.h(0p)exec(3p)getenv(3p)setenv(3p)