How do I extract a substring from string using a regular expression?

Question

I am new to regular expressions in Ruby.

The string looks something like http://www.site.com/media/pool/product_color_purple.jpg and I am trying to extract from this just the bit which has the colour in it. This can be a variable length, as some of the colours are like prince_purple.jpg.

So I have:

colour = c.attr('src').match(/(.*)color_(.*).jpg/)
puts "Colour is #{colour}"

What colour returns is the string again, instead of the extracted bit, which is the colour. What is going wrong here?

match returns MatchData and "mtch[0] is equivalent to the special variable $&, and returns the entire matched string. mtch[1], mtch[2], and so on return the values of the matched backreferences" - ruby-doc.org/core/classes/MatchData.html — Jonas Elfström
– Jonas Elfström, Commented Apr 27, 2011 at 11:25
Your link is broken. It's better to show here what you wanted to show. — sawa
– sawa, Commented Apr 27, 2011 at 15:47

Sector · Accepted Answer · 2011-04-27 11:33:23Z

14

str="http://www.site.com/media/pool/product_color_purple.jpg"
colour = str.match(/color_([^\/.]*).jpg$/)
puts "Colour is #{colour[1]}"

You not get "Colour is purple" because match returns MatchData, not string

edited Apr 27, 2011 at 11:33

answered Apr 27, 2011 at 11:24

Sector

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fl00r · Accepted Answer · 2011-04-27 11:22:10Z

3

url="http://www.site.com/media/pool/product_color_purple.jpg"
color = url.scan(/color_(.*).jpg/)[0][0]
#=> purple

or

url="http://www.site.com/media/pool/product_color_purple.jpg"
color = url.match(/color_(.*).jpg/)[1]
#=> purple

answered Apr 27, 2011 at 11:22

fl00r

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Comments

Jonas Elfström · Accepted Answer · 2011-04-27 11:22:49Z

2

Without Regexp as an example of another way to do it

url="http://www.site.com/media/pool/product_color_purple.jpg"
color = url[url.rindex("_")+1..-1].split(".")[0]

For this I would stick with regexp though.

color = url.match(/.*_(.*)\./)[1]

edited Apr 27, 2011 at 11:22

answered Apr 27, 2011 at 11:16

Jonas Elfström

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Michael Kohl · Accepted Answer · 2011-04-27 10:20:02Z

0

>> s = %w(http://www.site.com/media/pool/product_color_purple.jpg http://www.site.com/media/pool/product_color_prince_purple.jpg) 
#=> ["http://www.site.com/media/pool/product_color_purple.jpg", "http://www.site.com/media/pool/product_color_prince_purple.jpg"]
>> s.map { |c| c.match(/\w*_color_(\w+).jpg/)[1] } 
#=> ["purple", "prince_purple"]

answered Apr 27, 2011 at 10:20

Michael Kohl

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jazzdawg · Accepted Answer · 2011-04-27 10:30:45Z

0

You can try this regex.

/color_(.*)?.jpg/

answered Apr 27, 2011 at 10:30

jazzdawg

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