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I have a string like this:

var = "Renewal Quote RQ00041233 (Payment Pending) Policy R38A014294-1"

I have to extract "Payment Pending" from that string using only the information included in another single string.

The following:

var[/\((.*)\)/, 1]

will extract what I want. I can include the string representation of the regex in the string to be given, and construct the regular expression from it using Regexp.new, but I have no way to achieve the information 1 used as the second argument of [].

Without the second argument 1,

regex_string = '\((.*)\)'
var[Regexp.new(regex_string)]

fetches the string "(Payment Pending)"instead of the expected "Payment Pending".

Can someone help me?

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  • 1
    Not sure what you are trying to do. Will var[Regexp.new('\((.*)\)'), 1] not work? Commented Mar 6, 2019 at 7:16
  • 1
    I'd ask why you're having to pass regexes around as strings. Commented Mar 6, 2019 at 7:17
  • @sawa It will work, but I am asking Don't I have the way to convert the entire /\((.*)\)/, 1 into a regular expression? Commented Mar 6, 2019 at 7:19
  • @Schwern Because I have to read the regular expression from the sheet and use it in my program. Commented Mar 6, 2019 at 7:19
  • @sawa I have to write the regular expression into a single cell in Excel which I need to read and use it in my program. Commented Mar 6, 2019 at 7:20

3 Answers 3

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3

Not sure what you are trying to do, but you can get rid of capturing groups using a different regex:

var[/(?<=\().*(?=\))/]
# => "Payment Pending"

or

var[Regexp.new('(?<=\().*(?=\))')]
# => "Payment Pending"
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Comments

1

/\((.*)\)/ is just shorthand for Regexp.new('\((.*)\)').

String#[] takes a regex and a capture group as two separate arguments. var[/\((.*)\)/, 1] is var[Regex, 1].

The important thing to realize is 1 is passed to var[], not the regex.

re = Regexp.new('\((.*)\)')
match = var[re, 1]

Note: you might want to require a named capture group rather than a numbered one. It's very easy to accidentally include an extra capture group in a regex.

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7 Comments

You might want to add the conclusion of you argument. Perhaps: "so, it is impossible to do that" or "so, it does not make sense to try to do that."
yes, I am aware of that but I have to read the regular expression as a single string from the excel sheet and use it in my program, My program receives the argument inside Regex["]
@Schwern It is impossible/does not make sense to include the 1 information in the regex. Wasn't that your point?
@sawa I'd assumed it was a requirement that the list of regexes has to include a capture group.
@Rajagopalan Can you require that the regexes include a capture group?
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1

Assuming there are no nested parenthesis in the string, one way to do that without using a regular expression is as follows.

instance_eval "var[(i=var.index('(')+1)..var.index(')',i)-1]"
  #=> "Payment Pending"

See String#index, particularly the reference to the optional second argument, "offset".

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3 Comments

Your answer is educational, but you seem to be missing the point. The issue is to express the entire instruction in a single string.
@sawa, yes, I know.
Thank you. Another way, yes. But it has to be one single expression.

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