Odd behavior of String#scan

ruby-talk
1

First off, the problem I am trying to solve can be simplified down
to:

'abcSTARTdef,ghi,jkl,ENDmno'.scan(/START([^,]*,)*END/)

    What I want is [["def,"], ["ghi,"], ["jkl,"]] (or the same thing
without the commas), and I still need a way to achieve this. I can
accomplish it with:

'abcSTARTdef,ghi,jkl,ENDmno'.scan(/START(.*)END/)[0][0].split(/,/)

    But this does two operations where it seems like one should suffice.
Does someone know of a way to do this in a single operation?

    Back to the odd behavior, the first expression actually returns
[["jkl,"]]. I can't figure out how that is the correct answer by any
reasonable definition of "scan". However, the equivalent String#match
does the same kind of thing, so I must be missing something. Can
someone please explain this behavior?

    Thanks,

    - Warren Brown

2

Warren Brown wrote:

    First off, the problem I am trying to solve can be simplified down
to:

'abcSTARTdef,ghi,jkl,ENDmno'.scan(/START([^,]*,)*END/)

    What I want is [["def,"], ["ghi,"], ["jkl,"]] (or the same thing
without the commas), and I still need a way to achieve this. I can
accomplish it with:

'abcSTARTdef,ghi,jkl,ENDmno'.scan(/START(.*)END/)[0][0].split(/,/)

    But this does two operations where it seems like one should suffice.
Does someone know of a way to do this in a single operation?

I would suggest:

   'abcSTARTdef,ghi,jkl,ENDmno'.match(/START(.*)END/)[1].split(',')

I don't know of a way to accomplish it in one step. String#scan attempts to match the whole regex at multiple places within the string; but you need the START and END to delimit the substring over which scan operates.

    Back to the odd behavior, the first expression actually returns
[["jkl,"]]. I can't figure out how that is the correct answer by any
reasonable definition of "scan". However, the equivalent String#match
does the same kind of thing, so I must be missing something. Can
someone please explain this behavior?

Because you have this:

   ([^,]*,)*

The final * allows the group to match multiple times. The MatchData will hold only the last match however, which is "jkl,".

3

Will this do?
   
  s="abcSTARTdef,ghi,jkl,ENDmno"
  s.scan(/START(.*)END/).to_s.split(",")
   
  => ["def", "ghi", "jkl"]

···

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