How to cut string with ruby

I have strings:

до 100(прошло до 15 лет)
до 100 (прошл开发者_开发知识库о от 15 лет)
до 75
до 100 (10 лет)
до 100 (10 лет)

I want to cut strings like

до 100
до 100
до 75
до 100
до 100

strings = ['до 100(прошло до 15 лет)',
           'до 100 (прошло от 15 лет)',
           'до 75',
           'до 100 (10 лет)',
           'до 100 (10 лет)']

strings.map! { |str| str[/до \d+/] }

p strings    #=> ["до 100", "до 100", "до 75", "до 100", "до 100"]

There are a few different approaches to this. For example, you could cut off the string starting at the first (, if the string has one. However, I like this more explicit regular expression approach:

regex = /^до \d+/
str = "до 100(прошло до 15 лет)"
result = str[regex] # "до 100"

The regular expression /^до \d+/ matches instances of до and a series of digits that occur at the start of the string. The syntax str[regex] returns the first (and, in this case, only) match, or nil if there is no match.

How about something like:

cut = full.match(/^до \d*/)[0]

...that is, match anchored to start of the string the characters до, followed by any number of digits; return the whole matched part.