How can I replace and multiply dimensions of img tags in Perl or Ruby? - html

Question

I have a folder full of html files created for a Kindle ebook. The images are coded with width and height, as per the Kindle guidelines:
<img width="328" height="234" src="images/224p_fmt.jpeg" alt="224p.tif"/>
What I need to create/find is a script that will process all the image tags, multiply the width an height attributes by a specified amount (coded into the script) and write them back into the html files.
So, for the above example, say I want to multiply by 1.5, and wind up with
<img width="492" height="351" src="images/224p_fmt.jpeg" alt="224p.tif"/>
Scripts like this are not my forte, so help appreciated. I especially am unclear on how to write a script that I can run on file(s) from the command line and just input/output html.
I assume the meat of the code would be something like
s/<img width="([0-9]+)" height="([0-9]+)" src="(.*?)" alt=".*"/>/'<img width="'.$1*1.5.'" height="'.$2*1.5.'" src="'.$3.'" alt=""/>'/eg;
Which I realize is incorrect (the multiplication part) which is why help appreciated.

Answer 1

You've already got the main regex figured out, just need to tweak it and decide a language. Using regexes on html is not optimal, but since this is somewhat straightforward, its probably ok.
perl -pi.bak -we 's/<img width="([0-9]+)" height="([0-9]+)"/q(<img width=") .
$1*1.5 . q(" height=") . $2*1.5 . q(")/eg;' yourfile.html
Note the use of the alternate quoting q(...), since using single quotes on the command line will conflict with the shell quoting.
There's no need to touch any parts you're not changing, unless you feel the need to make a stricter match. If you do, you can add a look-ahead assertion:
(?=\s*src=".*?"\s*alt=".*?"\/>)
This part will remain unchanged by the substitution.

Answer 2

In Python I'd do it like this.
import sys, re
source = sys.stdin.read()
def multi(by):
def handler(m):
updated = int(m.group(2)) * by
return m.group(1) + str(updated)
return handler
print re.sub(r'((?:width|height)=["\'])(\d+)', multi(1.5), source)
Then you can handle input and output on the command like using < and >.
$ python resize.py < index.html > new_file.html

Answer 3

I would look into using the nokogiri gem to parse the HTML, search for image tags, extract the width and height attributes and then output the changed document so you can save it.
More information at the nokogiri tutorial page.

Answer 4

You're right, it can be done with a small Ruby script. It can look like this :
source = '<img width="328" height="234" src="images/224p_fmt.jpeg" alt="224p.tif"/>'
datas = source.scan(/<img width="([0-9]+)" height="([0-9]+)" src="(.*?)" alt=".*">/).flatten!
source.gsub!(data[0], (data[0].to_i * 1.5).to_s)
source.gsub!(data[1], (data[1].to_i * 1.5).to_s)
Of course, it's a quick and dirty script, far from perfect and it has some drawback.