File-local variables can be dangerous; when you visit someone else’s
file, there’s no telling what its local variables list could do to
your Emacs. Improper values of the
eval “variable”, and
other variables such as load-path, could execute Lisp code you
didn’t intend to run.
Therefore, whenever Emacs encounters file local variable values that are not known to be safe, it displays the file’s entire local variables list, and asks you for confirmation before setting them. You can type y or SPC to put the local variables list into effect, or n to ignore it. When Emacs is run in batch mode (see Initial Options), it can’t really ask you, so it assumes the answer n.
Emacs normally recognizes certain variable/value pairs as safe. For instance, it is safe to give comment-column or fill-column any integer value. If a file specifies only known-safe variable/value pairs, Emacs does not ask for confirmation before setting them. Otherwise, you can tell Emacs to record all the variable/value pairs in this file as safe, by typing ! at the confirmation prompt. When Emacs encounters these variable/value pairs subsequently, in the same file or others, it will assume they are safe.
Some variables, such as load-path, are considered particularly risky: there is seldom any reason to specify them as local variables, and changing them can be dangerous. If a file contains only risky local variables, Emacs neither offers nor accepts ! as input at the confirmation prompt. If some of the local variables in a file are risky, and some are only potentially unsafe, you can enter ! at the prompt. It applies all the variables, but only marks the non-risky ones as safe for the future. If you really want to record safe values for risky variables, do it directly by customizing ‘safe-local-variable-values’ (see Easy Customization).
The variable enable-local-variables allows you to change the
way Emacs processes local variables. Its default value is t,
which specifies the behavior described above. If it is
Emacs simply ignores all file local variables.
:safe means use
only the safe values and ignore the rest. Any other value says to
query you about each file that has local variables, without trying to
determine whether the values are known to be safe.
The variable enable-local-eval controls whether Emacs
eval variables. The three possibilities for the
variable’s value are t,
nil, and anything else, just as
for enable-local-variables. The default is
is neither t nor
nil, so normally Emacs does ask for
confirmation about processing
As an exception, Emacs never asks for confirmation to evaluate any
eval form if that form occurs within the variable