Question

I find myself constantly doing the same thing, using designers to create nice ui’s then convert HTML/CSS to split across the asset pipeline and find and replace paths and css+js tags; updating everything to use the asset path. Is there something that automagically does this?

Answer 1

To me, this situation just calls out loudly for sed. If you’re running Linux, Mac OS X, or another *nix, read on. (If your dev environment is Windows but you are deploying to *nix server where you can set up post-deploy scripts, this approach will still work there.)

So your designer has access to your assets in local directories, and it’ll generate tags like <img src="images/logo.png">. But, in deployment you want to either replace those paths with ERB calls like <img src="<%= asset_path 'logo.png' %>">, or else change them to point at some external CDN with a tag like <img src="http://assets.mysite.com/logo.png">, right?

Well, in either case, sed is your friend! Sed can (among other things) go through a file and apply regex substitutions to them in-place. In the ERB call situation (assuming you’ve already renamed your file to have an erb extension), you would run this command:

$ sed -i 's/\(<img[^>]*src="\)images/\([^"]+\)\("[^>*]>\)/\1<%= asset_path \'\2\' %>\3/g' somefile.html.erb

After running this command, somefile.html.erb will be using asset_path instead of manually specified image paths.

The second case, where you are providing images on another server or maybe just from another path, is similar:

$ sed -i 's/\(<img[^>]*src="\)images/\([^"]+\)\("[^>*]>\)/\1http:\/\/assets.mysite.com\/\2\3/g' somefile.html

And Bob’s your uncle!

One thing that’s annoying about these commands is that you have to run them on each and every file. Well, time for another UNIX utility to come to the rescue: find. This utility can run a script on a bunch of files in a directory tree:

$ find dir/with/html -type f -name '*.html.erb' -exec sed 's/foo/bar/g' {} \;

Now, if much of the above looks like ancient Latin to you (and you aren’t fluent in ancient Latin), you’ll want to go learn more about regular expressions, so that you can tweak the above commands to do the various different kinds of transformations you want. This is a pretty good guide to using sed and regular expressions that doesn’t assume much prior knowledge.

Once you have a set of commands that does the right thing, save them to a shell script file. Then, just run that file whenever you need it, and it will do all the annoying work for you! That’s what makes learning all these obtuse commands worth it; they’re more work upfront than a nice GUI find & replace dialog, but the flexibility of what they do and the ability to bundle them up into scripts saves you time and annoyance in the long run.