putenv(3) Library Functions Manual putenv(3)NAME
putenv - Sets an environment variable
LIBRARY
Standard C Library (libc.so, libc.a)
SYNOPSIS
#include <stdlib.h>
int putenv(
const char *string);
STANDARDS
Interfaces documented on this reference page conform to industry standards as follows:
putenv(): XPG4, XPG4-UNIX
Refer to the standards(5) reference page for more information about industry standards and associated tags.
PARAMETERS
Points to a name=value string.
DESCRIPTION
The putenv() function sets the value of an environment variable by altering an existing variable or by creating a new one. The new envi-
ronment variable remains in effect even after the program setting it is exited.
The string parameter points to a string of the form "name=value", where name is the environment variable and value is the new value for it.
NOTES
The putenv() function manipulates the environ external variable, and it can be used in conjunction with the getenv() function. However, the
third parameter to the main function (the environment pointer) is not changed.
The putenv() function uses the malloc() function to enlarge the environment.
A potential error is to call putenv() with an automatic variable as the argument and then exit the calling function while string is still
part of the environment.
RETURN VALUES
Upon successful completion, a value of 0 (zero) is returned. If the malloc() function is unable to obtain sufficient space to expand the
environment, the putenv() function returns a nonzero value.
RELATED INFORMATION
Functions: clearenv(3), exec(2), getenv(3), malloc(3)
Standards: standards(5) delim off
putenv(3)
Check Out this Related Man Page
PUTENV(3) Linux Programmer's Manual 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(): _SVID_SOURCE || _XOPEN_SOURCE
DESCRIPTION
The putenv() function adds or changes the value of environment variables. The argument string is of the form name=value. If name does not
already exist in the environment, 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 environment.
RETURN VALUE
The putenv() function returns zero on success, or nonzero if an error occurs.
ERRORS
ENOMEM Insufficient space to allocate new environment.
CONFORMING TO
SVr4, POSIX.1-2001, 4.3BSD.
NOTES
The putenv() function is not required to be reentrant, and the one in libc4, libc5 and glibc 2.0 is not, but the glibc 2.1 version is.
Description for libc4, libc5, glibc: If the argument string is of the form name, and does not contain an '=' character, then the variable
name is removed from the environment. If putenv() has to allocate a new array environ, and the previous array was also allocated by
putenv(), then it will be freed. In no case will the old storage associated to the environment variable itself be freed.
The libc4 and libc5 and glibc 2.1.2 versions conform to SUSv2: the pointer string given to putenv() is used. In particular, this string
becomes part of the environment; changing it later will change the environment. (Thus, it is an error is to call putenv() with an auto-
matic variable as the argument, then return from the calling function while string is still part of the environment.) However, glibc
2.0-2.1.1 differs: a copy of the string is used. On the one hand this causes a memory leak, and on the other hand it violates SUSv2. This
has been fixed in glibc 2.1.2.
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.
SEE ALSO clearenv(3), getenv(3), setenv(3), unsetenv(3), environ(7)COLOPHON
This page is part of release 3.25 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
GNU 2007-07-26 PUTENV(3)