Regular expression to match only the first file in a RAR file set

Question

To see what file to invoke the unrar command on, one needs to determine which file is the first in the file set.

Here are some sample file names, of which - naturall

Answer 1

The short answer is that it's not possible to construct a single regex to satisfy your problem. Ruby 1.8 does not have lookaround assertions (the (?

1) Use more than one regex to do it.

def is_first_rar(filename)
    if ((filename =~ /part(\d+)\.rar$/) == nil)
        return (filename =~ /\.rar$/) != nil
    else
        return $1.to_i == 1
    end
end

2) Use the regex engine for ruby 1.9, Oniguruma. It supports lookaround assertions, and you can install it as a gem for ruby 1.8. After that, you can do something like this:

def is_first_rar(filename)
    reg = Oniguruma::ORegexp.new('.*(?:(?