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
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
You can also tell Emacs to permanently ignore all the variable/value pairs in the file, by typing i at the confirmation prompt – these pairs will thereafter be ignored in this file and in all other files.
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 Interface).
Similarly, if you want to record values of risky variables that should
be permanently ignored, customize
enable-local-variables allows you to change the
way Emacs processes local variables. Its default value is
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.
:all instructs Emacs
to set all file local variables regardless of whether their value is
safe or not (we advise not to use this permanently). 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.
enable-local-eval controls whether Emacs
eval variables. The three possibilities for the
variable’s value are
nil, and anything else, just as
enable-local-variables. The default is
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