How to gsub a string with a concatenated value?

Question

I need to change the value of a parameter (OFFSET=) by adding 20 to its value. So instead of having OFFSET=0 I get OFFSET=20. Now, I can't be sure that the value for OFFSET is equal to 0, so I need to extract it. Here is what I have tried:

aNumber  = "myValue=20".match(/myValue=(\d+)/)[1].to_i
bString  = "OFFSET=#{aNumber}"
newValue = bString.gsub(/OFFSET=#{aNumber}/, "OFFSET=#{aNumber + 20}")

Now, to use #{} I obviously need a string with "" , which I can't use together with .gsub() or .match() . Right now I am not able to gsub because it can't get the value of aNumber . How can that be done?

Answer 1

You can use gsub with a block:

x = "myValue=20"
p x.gsub(/\d+/){|x| x.to_i + 20} # => myValue=20

or if you have a longer string and only want to change myValue:

x = "firstValue=10, myValue=20, otherValue=30"
p x.gsub(/(?<=myValue=)(\d+)/){|x|  x.to_i + 20} # => firstValue=10, myValue=40, otherValue=30