These functions set, unset and fetch environment variables from the host environment list. For compatibility with differing environment conventions, the given arguments name and value may be appended and prepended, respectively, with an equal sign "=".
The getenv function obtains the current value of the environment variable, name.
The setenv function inserts or resets the environment variable name in the current environment list. If the variable name does not exist in the list, it is inserted with the given value. If the variable does exist, the argument overwrite is tested; if overwrite is zero, the variable is not reset, otherwise it is reset to the given value.
The putenv function takes an argument of the form name=value and is equivalent to:
setenv(name, value, 1);
The unsetenv function deletes all instances of the variable name pointed to by name from the list.
The getenv function returns the value of the environment variable as a NUL -terminated string. If the variable name is not in the current environment, NULL is returned.
.Rv -std setenv putenv