How to combine Ruby regexp conditions

Question

I need to check if a string is valid image url. I want to check beginning of string and end of string as follows:

• Must start with http(s):
• Must end by .jpg|.png|.gif|.jpeg

So far I have:

(https?:)

I can't seem to indicate beginning of string \A, combine patterns, and test end of string.

Test strings:

"http://image.com/a.jpg"
"https://image.com/a.jpg"
"ssh://image.com/a.jpg"
"http://image.com/a.jpeg"
"https://image.com/a.png"
"ssh://image.com/a.jpeg"

Please see http://rubular.com/r/PqERRim5RQ

Using Ruby 2.5

Answer 1

Using your very own demo, you could use

^https?:\/\/.*(?:\.jpg|\.png|\.gif|\.jpeg)$

See the modified demo.

---

One could even simplify it to:

^https?:\/\/.*\.(?:jpe?g|png|gif)$

See a demo for the latter as well.

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This basically uses anchors (^ and $) on both sides, indicating the start/end of the string. Additionally, please remember that you need to escape the dot (\.) if you want to have ..

---

There's quite some ambiguity going on in the comments section, so let me clarify this:

^  - is meant for the start of a string 
     (or a line in multiline mode, but in Ruby strings are always in multiline mode)
$  - is meant for the end of a string / line
\A - is the very start of a string (irrespective of multilines) 
\z - is the very end of a string (irrespective of multilines) 

Answer 2

You may use

reg = %r{\Ahttps?://.*\.(?:png|gif|jpe?g)\z}

The point is:

1. When testing at online regex testers, you are testing a single multiline string, but in real life, you will validate lines as separate strings. So, in those testers, use ^ and $ and in real code, use \A and \z.
2. To match a string rather than a line you need \A and \z anchors
3. Use %r{pat} syntax if you have many / in your pattern, it is cleaner.

Online Ruby test:

urls = ['http://image.com/a.jpg',
        'https://image.com/a.jpg',
        'ssh://image.com/a.jpg',
        'http://image.com/a.jpeg',
        'https://image.com/a.png',
        'ssh://image.com/a.jpeg']
reg = %r{\Ahttps?://.*\.(?:png|gif|jpe?g)\z}
urls.each { |url|
    puts "#{url}: #{(reg =~ url) == 0}"
}

Output:

http://image.com/a.jpg: true
https://image.com/a.jpg: true
ssh://image.com/a.jpg: false
http://image.com/a.jpeg: true
https://image.com/a.png: true
ssh://image.com/a.jpeg: false