PUTENV(3P) POSIX Programmer's Manual PUTENV(3P)PROLOG
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.
NAMEputenv — change or add a value to an environment
SYNOPSIS
#include <stdlib.h>
int putenv(char *string);
DESCRIPTION
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 vari‐
able 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
Upon successful completion, putenv() shall return 0; otherwise, it
shall return a non-zero value and set errno to indicate the error.
ERRORS
The putenv() function may fail if:
ENOMEM Insufficient memory was available.
The following sections are informative.
EXAMPLES
Changing the Value of an Environment Variable
The following example changes the value of the HOME environment vari‐
able to the value /usr/home.
#include <stdlib.h>
...
static char *var = "HOME=/usr/home";
int ret;
ret = putenv(var);
APPLICATION USAGE
The putenv() function manipulates the environment pointed to by envi‐
ron, 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 applica‐
tion 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().
RATIONALE
Refer to the RATIONALE section in setenv().
FUTURE DIRECTIONS
None.
SEE ALSO
exec, free(), getenv(), malloc(), setenv()
The Base Definitions volume of POSIX.1‐2008, <stdlib.h>
COPYRIGHT
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 Electri‐
cal 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.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 PUTENV(3P)
