From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2008-11-20T22:17:06+09:00
Subject: Re: search reg-exp for exact match

On Thu, Nov 20, 2008 at 1:49 PM, John Butler <johnnybutler7@gmail.com> wrote:
> Hi,
>
> I have a regular expression
> /\b2003|\2004|\2005|\2006|\2007|\2008|\2009\b/
> and i want to check if various years are present.
>
> "2003" =~  /\b2003|\2004|\2005|\2006|\2007|\2008|\2009\b/
> returns 0 as expected
>
> "2010" =~  /\b2003|\2004|\2005|\2006|\2007|\2008|\2009\b/
> returns nil as expected
>
> But i want only exact matches so when i search for "2003 - 2008" i want
> nil returned as there is no exact match for that particular string.  I
> thought the \b would give me this but it doesnt.
>
> "2003 - 2008" =~  /\b2003|\2004|\2005|\2006|\2007|\2008|\2009\b/
> returns 0 i want nil returned.
>
> Anyone help?

To do exactly what you are asking for: you can anchor the regexp
to the beggining or end of the string:

irb(main):013:0> re = /\A(2003|2004|2005|2006|2007|2008|2009)\Z/
=> /\A(2003|2004|2005|2006|2007|2008|2009)\Z/
irb(main):014:0> "2003" =~ re
=> 0
irb(main):015:0> "2003 - 2008" =~ re
=> nil

In this case you don't need the \b anymore. BTW, you had typos there
because you had \2 instead of \b.
Anyway, if you want exact matches of strings you don't need regexps:

irb(main):018:0> years = (2003..2009).map {|x| x.to_s}
=> ["2003", "2004", "2005", "2006", "2007", "2008", "2009"]
irb(main):020:0> years.include? "2003"
=> true
irb(main):021:0> years.include? "2003 - 2008"
=> false

If you have many numbers and many lookups, a Set should be better,
performance-wise.
Now, if we are talking about ranges of years we can do even better:

irb(main):022:0> min_year = 2003
=> 2003
irb(main):023:0> max_year = 2009
=> 2009
irb(main):024:0> year_to_test = "2003".to_i
=> 2003
irb(main):025:0> min_year <= year_to_test and year_to_test <= max_year
=> true
irb(main):026:0> year_to_test = "2008".to_i
=> 2008
irb(main):027:0> min_year <= year_to_test and year_to_test <= max_year
=> true
irb(main):028:0> year_to_test = "2010".to_i
=> 2010
irb(main):029:0> min_year <= year_to_test and year_to_test <= max_year
=> false


Hope this helps,

Jesus.