Regex: img src urls that don't have multiple paths - html

Question

Going through another crazy website migration!
I have HTML img src urls that look like this
http://blog.example.com/imagename.jpg
Image formats can also be jpg, png, or gif
We need a regex that finds every url that has the domain then "/imagename.jpg" immediately after.
Very new to regex, what would the expression be?

Answer 1

Better Alternative for WordPress Migrations
If you are moving your website and you will want to replace all references to the old site with the new domain, I suggest you use David Coveney's Serialized Search & Replace DB v2.1.0. You'll want to run this on a new copy of the database, always have a backup handy. Import the database on the destination server, then run the tool - You don't even have to upload the server files.
When I do this coming from a development server to live domain, I usually do two search & replaces:
One for URLs, very basic:
Search: mywebsite.devserver.com
Replace: my-new-website.com
And one for file paths:
Search: /vhosts/devserver.com/mywebsite
Replace: /vhosts/my-new-website.com/httpdocs
(Note: This is assuming the majority of the file path is the same for both servers. Your search & replace paths may need to be more accurate)
The reason you want serialized search and replace is that some data is stored in PHP-serialized format, and if you change the value with a text editor or in MySQL directly, it may not be able to unserialize afterwards.
Regex Answer
Select images hosted by blog.example.com with the following regex pattern:
((http|https)://blog\.example.com/[^ \r\n]+\.(jpg|jpeg|png|gif))
Which basically searches for this: http(s)://blog.example.com/*.(jpg/png/etc)
Matches the URLs in the following examples:
http://example.com/imagename.jpg
http://blog.example.com/imagename.jpg
http://blog.example.com/favicon.png
http://blog.example.com/uploads/2013/05/kitten.gif
https://blog.example.com/ssl-secure.png
This is my favorite gif https://blog.example.com/some-hilarious-image.gif hahaha
DOES NOT match any of these:
blog.example.com/google.png
https://blog.google.com/google.png
our website is http://blog.example.com and has an image named /imagename.png
http://blog.example.com/
WHY it doesn't match those (by line):
Does not include http(s)://
Hosted by google
Paragraph text, where the URL is split into two parts
Not an image
$1 returns the full URL of the image.
I tested this on RegexTester.com. You can copy the pattern in the top field, and all of the examples in the box below. The red highlights are matches.

Answer 2

Many good suggestions already, and why would a wordpress site hardcode domain name to links, but thats not our problem right now. If you need a regex then try this:
(?<=<img).+(?<=src=["'])(.+(?:jpe?g|gif|png))
EXPLAINED:
(?<=<img).+(?<=src=["']) - be sure we're inside an <img> tag up to src attribute
(.+(?:jpe?g|gif|png)) capture everything up to required extension