setenv - change or add an environment variable
The setenv() function adds the variable
name to the environment with the value
name does not already exist. If
name does exist in the environment, then its value is changed to
overwrite is nonzero; if
overwrite is zero, then the value of
name is not changed (and setenv() returns a success status). This function makes copies of the strings pointed to by
value (by contrast with putenv(3)).
The unsetenv() function deletes the variable
name from the environment. If
name does not exist in the environment, then the function succeeds, and the environment is unchanged.
name is NULL, points to a string of length 0, or contains an '=' character.
Insufficient memory to add a new variable to the environment.
POSIX.1-2001, POSIX.1-2008, 4.3BSD.
POSIX.1 specifies that if
name contains an '=' character, then setenv() should fail with the error EINVAL; however, versions of glibc before 2.3.4 allowed an '=' sign in
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