Strange behavior of String.scan

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?

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”]

Alex Y. [email protected] 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?

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

Daniel DeLorme [email protected] 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.

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

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. :slight_smile:

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

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