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 correspond-
ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
NAME
putenv - 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
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 space used by string is no longer used once a new string which defines name is passed to putenv().
The putenv() function need not be reentrant. A function that is not required to be reentrant is not required to 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 variable 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 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.
The setenv() function is preferred over this function.
RATIONALE
The standard developers noted that putenv() is the only function available to add to the environment without permitting memory leaks.
FUTURE DIRECTIONS
None.
SEE ALSO
exec(), getenv(), malloc(), setenv(), the Base Definitions volume of IEEE Std 1003.1-2001, <stdlib.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .
IEEE
/The Open Group 2003 PUTENV(3P)