Can I use Emacs as pipe-thru formatter?

Can I use Emacs as pipe-thru formatter?

[Irving Kimura]

I'm writing a Perl script that, among other things, needs to pretty
print JavaScript code.  The formatting produced by the Emacs module
javascript-mode.el would be adequate for my purposes, but I don't
know how to apply it from within a Perl program.

(I'm sure that this is trivial to do from within an Emacs Lisp
script, but I am not very handy in this language, and besides, the
task is part of a much larger Perl program, so I would prefer to
do this from within Perl.)

Since, under Unix at least, it's not too difficult for a Perl script
to pipe a string through an external program, one possible way to
do what I want to do would be to write an "Emacs pipe" that somehow
uses javascript-mode.el to pretty print its stdin and spits the
results to stdout:

  % cat ugly.js | emacs_js_pretty_printer > pretty.js

But I have no idea about how to write such a pipe.  I would greatly
appreciate any help or advice on how to do this, or any other ideas
on how to tackle this problem.

Many thanks!

	-Irv

Re: Can I use Emacs as pipe-thru formatter?

[Barry Margolin]

In article <bgoebt$gf0$1@reader1.panix.com>,
Irving Kimura  <irving_kimura@lycos.com> wrote:
>Since, under Unix at least, it's not too difficult for a Perl script
>to pipe a string through an external program, one possible way to
>do what I want to do would be to write an "Emacs pipe" that somehow
>uses javascript-mode.el to pretty print its stdin and spits the
>results to stdout:
>
>  % cat ugly.js | emacs_js_pretty_printer > pretty.js
>
>But I have no idea about how to write such a pipe.  I would greatly
>appreciate any help or advice on how to do this, or any other ideas
>on how to tackle this problem.

Someone asked almost the same question a week or two ago.

Emacs doesn't read and write stdin/stdout, so it can't be used as a filter
in a pipeline.  But you can use -batch and -eval to make it run a function
and then exit, so you could have it read ugly.js into a buffer, format it,
and then write the result out to pretty.js.

-- 
Barry Margolin, barry.margolin@level3.com
Level(3), Woburn, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.

Re: Can I use Emacs as pipe-thru formatter?

[Kevin Rodgers]

Irving Kimura wrote:

> Since, under Unix at least, it's not too difficult for a Perl script
> to pipe a string through an external program, one possible way to
> do what I want to do would be to write an "Emacs pipe" that somehow
> uses javascript-mode.el to pretty print its stdin and spits the
> results to stdout:
> 
>   % cat ugly.js | emacs_js_pretty_printer > pretty.js

Try this:


emacs --batch \
	ugly.js \
	-f javascript-mode \
	--eval '(indent-region (point-min) (point-max) nil)' \
	--eval '(write-file "pretty.js")'

-- 
Kevin Rodgers

Re: Can I use Emacs as pipe-thru formatter?

[Oliver Scholz]

Barry Margolin <barry.margolin@level3.com> writes:

> Emacs doesn't read and write stdin/stdout, so it can't be used as a filter
> in a pipeline.  

Well, indeed you can not get a buffer from stdin (AFAICS). But you do
have some limited options. `print' for example prints to stdout in
batch-mode and `read' reads from stdin.

emacs -q --batch --eval '(print "hello")'

emacs -q --batch --eval '(princ (progn (insert initial-scratch-message) (buffer-substring (point-min) (point-max))))'

echo "\"lirum larum\"" | emacs -q --batch --eval '(message (read))'

Of course also:

echo '(print "Hello")' | emacs -q --batch --eval '(eval (read))'

There is even some interactivity possible:

emacs -q --batch --eval '(progn (find-file "~/.emacs") (if (y-or-n-p "Shall I print your .emacs? ") (print (buffer-substring (point-min) (point-max))) (print "O.k. Bye.")))'

    Oliver 
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