# Strange behavior of String.scan **URL:** \ **Category:** Ruby\ **Created:** [May 27, 2007, 9:55am UTC](https://www.ruby-forum.com/t/strange-behavior-of-string-scan/105210 "2007-05-27T09:55:37Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![HSSSSvard\_Moen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/b19c9b/32.png) [@HSSSSvard\_Moen](https://www.ruby-forum.com/u/HSSSSvard_Moen)\ **Post date:** [May 27, 2007, 9:55am UTC](https://www.ruby-forum.com/t/strange-behavior-of-string-scan/105210/1 "2007-05-27T09:55:37Z")
When I use String.scan with a block and just one group the result ends up as an array. More than one group works as expected. A small example to demonstrate: –ruby code start– data = ’ lb method member observed monitor all http member 192.168.1.68:http’ data.scan(/monitor all (._)$/) do |monitor| puts monitor.inspect end data.scan(/member ([0-9.]+):(._)/) do |adress, port| puts adress.inspect puts port.inspect end –ruby code end– gives me: [“http”] “192.168.1.68” “http” I’m running: ruby 1.8.6 (2007-03-13 patchlevel 0) [i486-linux] Is there something I have done wrong, or is this a bug? ---
**Author:** ![HSSSSvard\_Moen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/b19c9b/32.png) [@HSSSSvard\_Moen](https://www.ruby-forum.com/u/HSSSSvard_Moen)\ **Post date:** [May 27, 2007, 10:17am UTC](https://www.ruby-forum.com/t/strange-behavior-of-string-scan/105210/2 "2007-05-27T10:17:39Z")
HÃ¥vard Moen wrote: > end > data.scan(/member ([0-9.]+):(.\*)/) do |adress, port| > puts adress.inspect > puts port.inspect > end > –ruby code end– > > gives me: > [“http”] > “192.168.1.68” > “http” That’s expected. What scan actually yields to the block is an array, and in your second example that array is being automatically split into its component parts because you’ve given more than one block parameter in the pipes. A third example should make it clear: irb(main):004:0\> data.scan(/member ([0-9.]+):(._)/) do |match| irb(main):005:1_ puts match.inspect irb(main):006:1\> end [“192.168.1.68”, “http”] ---
**Author:** ![HSSSSvard\_Moen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/b19c9b/32.png) [@HSSSSvard\_Moen](https://www.ruby-forum.com/u/HSSSSvard_Moen)\ **Post date:** [May 27, 2007, 10:46am UTC](https://www.ruby-forum.com/t/strange-behavior-of-string-scan/105210/3 "2007-05-27T10:46:40Z")
Alex Y. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > puts monitor.inspect > > “http” Ok, but is there a way to get just the string without using something like monitor = monitor[0] at the start of the block? ---
**Author:** ![HSSSSvard\_Moen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/b19c9b/32.png) [@HSSSSvard\_Moen](https://www.ruby-forum.com/u/HSSSSvard_Moen)\ **Post date:** [May 27, 2007, 11:21am UTC](https://www.ruby-forum.com/t/strange-behavior-of-string-scan/105210/4 "2007-05-27T11:21:44Z")
HÃ¥vard Moen wrote: > Ok, but is there a way to get just the string without using something > like monitor = monitor[0] at the start of the block? You can use a comma to force the array to be parallel-assigned instead of single-assigned: data.scan(/monitor all (.\*)$/) do |monitor,| puts monitor.inspect end Daniel ---
**Author:** ![HSSSSvard\_Moen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/b19c9b/32.png) [@HSSSSvard\_Moen](https://www.ruby-forum.com/u/HSSSSvard_Moen)\ **Post date:** [May 27, 2007, 11:45am UTC](https://www.ruby-forum.com/t/strange-behavior-of-string-scan/105210/5 "2007-05-27T11:45:49Z")
Daniel DeLorme [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > HÃ¥vard Moen wrote: > > > Ok, but is there a way to get just the string without using something > > like monitor = monitor[0] at the start of the block? > > You can use a comma to force the array to be parallel-assigned instead > of single-assigned: > > data.scan(/monitor all (.\*)$/) do |monitor,| > puts monitor.inspect > end Great, thanks. ---
**Author:** ![HSSSSvard\_Moen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/b19c9b/32.png) [@HSSSSvard\_Moen](https://www.ruby-forum.com/u/HSSSSvard_Moen)\ **Post date:** [May 27, 2007, 11:25am UTC](https://www.ruby-forum.com/t/strange-behavior-of-string-scan/105210/6 "2007-05-27T11:25:44Z")
On 27.05.2007 10:17, Alex Y. wrote: > > puts monitor.inspect > > “http” > > That’s expected. What scan actually yields to the block is an array, > and in your second example that array is being automatically split into > its component parts because you’ve given more than one block parameter > in the pipes. A third example should make it clear: > > irb(main):004:0\> data.scan(/member ([0-9.]+):(._)/) do |match| > irb(main):005:1_ puts match.inspect > irb(main):006:1\> end > [“192.168.1.68”, “http”] irb(main):001:0\> “abc”.scan(/abc/) {|m| p m} “abc” =\> “abc” irb(main):002:0\> “abc”.scan(/(a)bc/) {|m| p m} [“a”] =\> “abc” irb(main):003:0\> “abc”.scan(/(a)(b)c/) {|m| p m} [“a”, “b”] =\> “abc” robert ---
**Author:** ![HSSSSvard\_Moen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/b19c9b/32.png) [@HSSSSvard\_Moen](https://www.ruby-forum.com/u/HSSSSvard_Moen)\ **Post date:** [May 27, 2007, 1:26pm UTC](https://www.ruby-forum.com/t/strange-behavior-of-string-scan/105210/7 "2007-05-27T13:26:00Z")
On 27.05.2007 11:44, Håvard Moen wrote: > > > data.scan(/monitor all (.\*)$/) do |monitor| > > > “192.168.1.68” > > Ok, but is there a way to get just the string without using something > like monitor = monitor[0] at the start of the block? Use only capturing groups for what you want to capture. For all others use non capturing groups. This sounds trivial but it’s actually as easy as that. 🙂 In case you haven’t seen non capturing groups yet: irb(main):002:0\> “cababab”.scan(/(.)(?:ab)+/) {|m| p m} [“c”] =\> “cababab” Kind regards robert