Inconsistent behavior in Ruby gsub replacement?

Question

The two gsub's yield different outcomes. Can anybody explain why? Code is also available at https://gist.github.com/franklsf95/6c0f8938f28706b5644d. ``` ver = 9999 str = " CFBundleDevelopmentRegion en CFBundleVersion 0.1.190 AppID 000000000000000" puts str.gsub /(CFBundleVersion .*\.).*()/, "#{$1}#{ver}#{$2}" puts '--------' puts str.gsub /(CFBundleVersion .*\.).*()/, "#{$1}#{ver}#{$2}" ``` My ruby version is `ruby 2.1.2p95 (2014-05-08 revision 45877) [x86_64-darwin13.0]` (MRI). On my machine, the outcome is: ``` CFBundleDevelopmentRegion en 9999 AppID 000000000000000 -------- CFBundleDevelopmentRegion en CFBundleVersion 0.1.9999 AppID 000000000000000 ``` The second one is the desired effect, but the firs…

Accepted Answer

It has to do with timing and how ruby regexes work. `gsub` sets `$1` and `$2`, but not until after it completes. So when you run the first time through, they're blank. When you run the second time, they were set by the previous `gsub`. If you want to do regex captures in place, you need `\1` and `\2`, like this: ``` puts str.gsub /(CFBundleVersion .*\.).*()/, '\1' + ver.to_s + '\2' ```

Inconsistent behavior in Ruby gsub replacement?

Solution

Problem