The command-line option ‘-batch’ causes Emacs to run noninteractively. In this mode, Emacs does not read commands from the terminal, it does not alter the terminal modes, and it does not expect to be outputting to an erasable screen. The idea is that you specify Lisp programs to run; when they are finished, Emacs should exit. The way to specify the programs to run is with ‘-l file’, which loads the library named file, or ‘-f function’, which calls function with no arguments, or ‘--eval=form’.
Any Lisp program output that would normally go to the echo area,
either using message, or using prin1, etc., with
t as the stream (see Output Streams), goes instead to
Emacs’s standard descriptors when in batch mode: message writes
to the standard error descriptor, while prin1 and other print
functions write to the standard output. Similarly, input that would
normally come from the minibuffer is read from the standard input
descriptor. Thus, Emacs behaves much like a noninteractive
application program. (The echo area output that Emacs itself normally
generates, such as command echoing, is suppressed entirely.)
Non-ASCII text written to the standard output or error descriptors is
by default encoded using locale-coding-system (see Locales)
if it is non-nil; this can be overridden by binding
coding-system-for-write to a coding system of you choice
(see Explicit Encoding and Decoding).
In batch mode, Emacs will enlarge the value of the
gc-cons-percentage variable from the default of ‘0.1’ up to
‘1.0’. Batch jobs that are supposed to run for a long time
should adjust the limit back down again, because this means that less
garbage collection will be performed by default (and more memory
consumed).
This variable is non-nil when Emacs is running in batch mode.
If Emacs exits due to signaling an error in batch mode, the exit status of the Emacs command is non-zero:
$ emacs -Q --batch --eval '(error "foo")'; echo $? foo 255