Accessing an array element or return an empty string

Question

When the following regular expression match yields no matching captures, accessing the element [1] will return the following error:

"".match(/(abc)/)[1]

returns the following error:

NoMethodError: undefined method `[]' for nil:NilClass

Is there a more concise single line implementation to perform the equivalent?

result = "".match(/(abc)/).nil? ? "" : "".match(/(abc)/)[1]

I am looking for a solution that does not require having to repeat the matching code **"".match(/abc/)** and yet safely access the first captured group or fail with an empty string as result.

[edited to be clearer]

For the following string, the match will be "123":

"abc123def".match(/abc([0-9]*)/)[1] => "123"

and "abcdef" should return ""

Aleksei Matiushkin · Accepted Answer · 2017-02-14 07:25:13Z

5

Yes, it is String#[] with regular expression as an argument.

""[/abc/]

For the example given:

"abc123def"[/(?<=abc)[0-9]*/]
#⇒ "123"

edited Feb 14, 2017 at 7:25

answered Feb 14, 2017 at 6:23

Aleksei Matiushkin

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5 Comments

tadman Over a year ago

String#[] is always presumed to be for things like substrings but it's also quite flexible.

Mark Kang Over a year ago

Apologies for not being clear. But:"abc123def"[/abc([0-9]*)/] => "abc123" "abc123def".match(/abc([0-9]*)/)[1] => "123"

Aleksei Matiushkin Over a year ago

Please see a comment: you are using a wrong regexp there.

Mark Kang Over a year ago

Thank you very much

Stefan Over a year ago

@MarkKang you can also pass the index of a capture group as the second argument to String#[], e.g: "abc123def"[/abc([0-9]*)/, 1]

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