CODEWITHSUNDEEP
rubyregexstring
Parimal
Parimal

Reputation: 326

Regex for optional quotes, array of hashes and empty string

I want to write a regular expression for accepting the following types in ruby -

1) "value1"

2) 'value2'

3) "" or ''

4) [{:this => :that, "that" => :this}, {'foo' => :bar}, {:bar => 'foo'}]

So far, I have the following -

regex = /(["']?)([^'"].*?[^'"])\1/

The problem with that is it does not accept the empty strings - "" and ''.

Can you suggest any alternative or improvement?

Upvotes: 0

Views: 271

Answers (1)

Lucas Trzesniewski
Lucas Trzesniewski

Reputation: 51330

I don't know what regex flavor ruby uses, but assuming it's somewhat Perl-compatible:

regex = /(["'])(?:\\.|.)*?\1/

Demo: http://regex101.com/r/iP8hY8/1

This expression will allow you to escape quotes in your string "like \" that".

The trick here is to use an alternative in such a way that the second part of the alternative (the .) will never be able to match a backslash. And the non-greedy quantifier ensures the backreference will match the ending quote first.

EDIT: Actually, I think I misread the 4th point in your question.

If you want the regex to match arrays of values, you'd have to create something more... parser-like, like this:

(?<value>
  (?<string>(?<quote>["'])(?:\\.|.)*?\k<quote>|:\w+)
|
  (?<hash>\{
    (?:(?:(?<hashitem>\s*\g<string>\s*=>\s*\g<value>\s*),\s*)*\g<hashitem>
    |\s*)
  \})
|
  \[
    (?:(?:\s*\g<value>\s*,\s*)*\g<value>
    |\s*)
  \]
)

Demo: http://regex101.com/r/iP8hY8/2

This expression will actually mach arrays of strings too. Note that I didn't include anything for numbers since you don't mention them.

If you specifically want to only match arrays of hashes, then you can tweak the above expression a bit:

(?<value>
  (?<string>(?<quote>["'])(?:\\.|.)*?\k<quote>|:\w+)
|
  (?<hash>\{
    (?:(?:(?<hashitem>\s*\g<string>\s*=>\s*\g<value>\s*),\s*)*\g<hashitem>
    |\s*)
  \})
|
  \[
    (?:(?:\s*\g<hash>\s*,\s*)*\g<hash>
    |\s*)
  \]
)

I'll let you further tweak this to your needs.

Upvotes: 1

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