an environment list (eg, as returned from g_get_environ()), or %NULL for an empty environment list
the environment variable to get
the value of the environment variable, or %NULL if the environment variable is not set in @envp. The returned string is owned by @envp, and will be freed if @variable is set or unset again.
2.32
Returns the value of the environment variable @variable in the provided list @envp.