pass variable to coffeescript

Question

from command line, how to pass a variable to coffeescript, so it can replace a corresponding placeholder, something like this:

$ echo "module.exports = {version: '$VERSION'}" | coffee -p -s VERSION=0.0.0

Expected JS:

(function() {

  module.exports = {
    version: '0.0.0'
  };

}).call(this);

Thank you

CoffeeScript alone won't do this for you. This question has some discussion of preprocessors that could run either before or after coffee. — Aaron Dufour
– Aaron Dufour, Commented May 3, 2012 at 12:41

abernier · Accepted Answer · 2012-05-03 02:01:21Z

3

Two things:

You need to define VERSION in the echo, not in the coffeescript compiler; by the time the coffeescript compiler sees it it's already translated $VERSION into ''.
echo is a shell builtin, and therefore the standard VERSION=0.0.0 echo "$VERSION" construct doesn't work.

So you want to create a new subshell so that the setting of VERSION doesn't propagate into your main shell, then perform the echo and coffee, like so:

$ (VERSION=0.0.0; echo "module.exports = {version: '$VERSION'}" | coffee -ps)       
(function() {

  module.exports = {
    version: '0.0.0'
  };

}).call(this);

The parentheses around the expression stop VERSION from being set:

$ echo $VERSION                                                              

$

edited May 3, 2012 at 2:01

abernier

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answered May 3, 2012 at 0:42

Venge

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1 Comment

abernier Over a year ago

Ok, my example is probably too simple... Your trick works well but it's rather a shell rather a coffee one. What if I want to compile a whole folder: coffee -c -o lib/ src/ but with VERSION=0.0.0 so $VERSION placeholder is replaced somewhere in src/? Thanks

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