URL manipulation: http://example.com/foo.jpg -> http://example.com/foo.preview.png

In rails I want to wrote some code to change this url string

https://img.skitch.com/20101222-kg5chjx4jetgcdeaug46hi6jpk.jpg

to

https://img.skitch开发者_运维技巧.com/20101222-kg5chjx4jetgcdeaug46hi6jpk.preview.png

Should I use regular Expression to change it?

I'm new to Regexp, anyone can show me how to do this, and how to learn this stuff

thanks

---

If the extension is of fixed length, you're better off using string slicing.

url = "https://img.skitch.com/20101222-kg5chjx4jetgcdeaug46hi6jpk.jpg"
print url[0..-5] + ".preview" + url[-4..-1]

outputs

https://img.skitch.com/20101222-kg5chjx4jetgcdeaug46hi6jpk.preview.jpg

Or if your extensions are of variable length you can use rindex() to find the start of the extension.

url = "https://img.skitch.com/20101222-kg5chjx4jetgcdeaug46hi6jpk.jpeg"
dot_index = url.rindex(".")-1
print url[0..dot_index] + ".preview" + url[dot_index+1..-1]

outputs

https://img.skitch.com/20101222-kg5chjx4jetgcdeaug46hi6jpk.preview.jpeg

If you must use a regex then do it like this:

url = "https://img.skitch.com/20101222-kg5chjx4jetgcdeaug46hi6jpk.jpeg"
print url.gsub(/\.(\w{2,4})$/, ".preview.\\1")

outputs

https://img.skitch.com/20101222-kg5chjx4jetgcdeaug46hi6jpk.preview.jpeg

---

If you're sure the file ends with .jpg, you can to

url = "https://img.skitch.com/20101222-kg5chjx4jetgcdeaug46hi6jpk.jpg"
url.gsub(".jpg", ".preview.jpg")

Otherwise, you can get the filename, then append the extension.

url = "https://img.skitch.com/20101222-kg5chjx4jetgcdeaug46hi6jpk.jpg"
ext = File.extname(url)
url.gsub(ext, ".preview{ext}")

---

A string replace seems to be enough. ".jpg" -> ".preview.png" Unfortunately I do not know ruby. In python it'll be

new_url = url.replace(".jpg",".preview.png",1)

I think that it'll be similar in ruby. It seems to be sub() instead.

new_url = url.sub(".jpg",".preview.png")