Ruby Regex Matchdata to Integer Conversion
I Have a String, Populated from the *Nix "Hostname" Command, That I Need to Parse for a Number. That's the Easy Part. the Difficulty Comes from a Need to Have...
I have a string, populated from the *nix "hostname" command, that I need to parse for a number. That's the easy part. The difficulty comes from a need to have to Do Math(tm) on that captured number. Apparently regex captures are always of type MatchData, which doesn't have any math functions like 'add' or 'modulo', nor does it have a method for ".to_i". Currently, in order to Do Math(tm) on my captured number I need to use MatchData's .to_s method to convert the capture to a string, then use String's .to_i to make it an integer. My question is, what's the better way to do this?
hostname = "webserver1337.mycorp.com"
number = hostname.match(/[a-z]+/)
puts "#{number}, with class #{number.class}" # prints '1337, with class MatchData'
somevar = number + 1 # this will fail horribly
temp1 = number.to_s
number = temp1.to_i
someothervar = number + 1
puts "#{number}, #{someothervar} with class #{number.class}" # prints '1337, 1338 with class FixNum'
This is... slightly ugly. Is there a better/cleaner way to achieve the same thing?
4 Answers
The MatchData object will return the string(s) contained in the match by using []. For example:
hostname = "webserver1337.mycorp.com"
m = hostname.match( /([a-z]+)(\d+)/ )
number = m[2].to_i + 1
p m[0], m[1], m[2], number
To do it one shot:
number = hostname.match(/\d+/)[0].to_i + 1
hostname = "webserver1337.mycorp.com"
number = hostname[/\d+/].to_i + 1
All data extract from a regexp are define like a string because it's extract from a String. Even if you extract digit data explicit
"webserver1337.mycorp.com" =~ /(\d+)/
p $1 #=> "1337"
puts $1.class #=> String
The top match would not handle a hostname with a number in the middle. i.e. foo23bar03 or 32bar30 would get the wrong number.
something like anchors the number match to the word boundary and gets the number out reliably:
number = hostname.match(/(\d+\b)/)[0]
building on this I made:
#!/bin/env ruby
# simple test of hostname parser
class Hostname
attr_reader :name, :number, :full_name
def initialize(hostname)
parse = hostname.match(/([A-Za-z0-9\-\_]+[A-Za-z\-\_]+)(\d+\b)/).to_a || []
@full_name = parse.fetch(0, hostname)
@name = parse.fetch(1, hostname)
@number = parse.fetch(2, hostname).to_i
end
end
I wrote specs for it and output up at this gist:
I believe it could be shorter with a negative match instead of a positive match, but this seemed to get it done for me!
Robert Thorne covers electric vehicle innovations, autonomous driving systems, global mobility trends, and automotive engineering developments.
