PUTENV(3) Linux Programmer's Manual PUTENV(3)
NAME
putenv - change or add an environment variable
SYNOPSIS
#include <stdlib.h>
int putenv(char *string(3,n));
DESCRIPTION
The putenv() function adds or changes the value of environment vari-
ables. The argument string(3,n) is of the form name=value. If name does
not already exist in(1,8) the environment, then string(3,n) is added to the envi-
ronment. If name does exist, then the value of name in(1,8) the environment
is changed to value. The string(3,n) pointed to by string(3,n) becomes part of
the environment, so altering the string(3,n) changes the environment.
RETURN VALUE
The putenv() function returns zero on success, or -1 if(3,n) an error(8,n)
occurs.
ERRORS
ENOMEM Insufficient space to allocate new environment.
NOTES
The putenv() function is not required to be reentrant, and the one in(1,8)
libc4, libc5 and glibc2.0 is not, but the glibc2.1 version(1,3,5) is.
Description for libc4, libc5, glibc: If the argument string(3,n) 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 asso-
ciated to the environment variable itself be freed.
The libc4 and libc5 and glibc 2.1.2 versions conform to SUSv2: the
pointer string(3,n) given to putenv() is used. In particular, this string(3,n)
becomes part of the environment; changing it later will change the
environment. (Thus, it is an error(8,n) is to call putenv() with an auto-
matic variable as the argument, then return from the calling function
while string(3,n) is still part of the environment.) However, glibc
2.0-2.1.1 differs: a copy of the string(3,n) is used. On the one hand this
causes a memory leak, and on the other hand it violates SUSv2. This has
been fixed in(1,8) glibc2.1.2.
The BSD4.4 version(1,3,5), like glibc 2.0, uses a copy.
SUSv2 removes the `const' from the prototype, and so does glibc 2.1.3.
CONFORMING TO
SVID 3, POSIX, BSD 4.3
SEE ALSO
clearenv(3), getenv(3), setenv(3), unsetenv(3), environ(5)
GNU 1993-04-08 PUTENV(3)