exec_cwd is a function to determine a current working directory for exec actions.

scope_cwd is function that determines the unit's scope.

exec_env is a function to determine an environement for exec actions.

exec is an action that B0_std.Os.Exit.exec's a unit's outcome as follows:

• The executed file is the unit's B0_meta.exe_file.
• The arguments have B0_std.Fpath.basename of B0_meta.exe_file as the program name and the action's args as arguments.
• If the unit defines exec_cwd, it is used to determine the cwd otherwise the default of B0_std.Os.Exit.exec is used.
• If the unit defines exec_env, it is used to determine the environment otherwise the default B0_std.Os.Exit.exec is used.

exec_file u file argv is a B0_std.Os.Exit.exec with file and argv and:

• If the unit u defines exec_cwd, it is used to determine the cwd otherwise the default of B0_std.Os.Exit.exec is used.
• If the unit u defines exec_env, it is used to determine the environment otherwise the default B0_std.Os.Exit.exec is used.