putenv - change or add value to environment
int putenv (char *string);
string points to a string of the form ``name<b>=value.'' putenv makes 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 becomes part of the environment, so altering the
string will change the environment. The space used by string is no
longer used once a new string-defining name is passed to putenv. Because
of this limitation, string should be declared static if it is declared
within a function.
exec(2), getenv(3C), malloc(3C), environ(5).
putenv returns non-zero if it was unable to obtain enough space via
malloc for an expanded environment, otherwise zero.
putenv manipulates the environment pointed to by environ<b>, and can be used
in conjunction with getenv. However, envp (the third argument to main)
is not changed.
This routine uses malloc(3C) to enlarge the environment.
After putenv is called, environmental variables are not in alphabetical
order. A potential error is to call the function putenv with a pointer
to an automatic variable as the argument and to then exit the calling
function while string is still part of the environment.
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