CODEWITHSUNDEEP
rubyregex
binarymason
binarymason

Reputation: 1433

Possible to pass variable to regex literal then capture match group to another local variable?

In order to save regex capture groups to a local variable, the regex must be on the left side of an operation such as /(?<somegroup>someregex)/ =~ 'somestring'. For example, given a url string, extracting the top level domain: 

/(?<extract>\b.com\b)[\/]{0,1}/ =~ 'google.com'
puts extract # => .com

There are various domains (.org, .scb, .wine, .me, etc). My strategy is to store all possible tlds from a reputable source in an array, and iterate through each one and pass it to the regex. How do you pass a variable to the literal?

Here is a simplified method of what I am trying to do:

def example_extract(url_str)
  exmpl = '.com'
  regx = /(?<extract>\b#{exmpl}\b)[\/]{0,1}/
  regx =~ url_str
  extract
end

example_extract('google.com')
# => NameError: undefined local variable or method `extract' for main:Object

I fail to pass a variable to a left hand (literal) regex operation. Why is my capture group extract not defined?

Upvotes: 1

Views: 98

Answers (2)

binarymason
binarymason

Reputation: 1433

For anyone's future reference. You have to use regexp's MatchData. This is what worked for me:

def example_extract(url_str)
  exmpl = '.com'
  regx = /(?<extract>\b#{exmpl}\b)[\/]{0,1}/
  extract = regx.match(url_str)[:extract]
  p extract
end

example_extract('google.com')

Upvotes: 0

sawa
sawa

Reputation: 168071

Under the documentation for Regexp#=~, it says:

This assignment is implemented in the Ruby parser. The parser detects ‘regexp-literal =~ expression’ for the assignment. The regexp must be a literal without interpolation and placed at left hand side.

The reason local variable was not assigned is because your regex was defined using interpolation, and is not a literal.

As the citation implies, assigning a local variable is done during parsing phase, and since string interpolation is done during run time, there seems no way to detour the limitation imposed by the specification.

Upvotes: 1

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