# Search reg-exp for exact match **URL:** \ **Category:** Ruby\ **Created:** [November 20, 2008, 1:53pm UTC](https://www.ruby-forum.com/t/search-reg-exp-for-exact-match/153722 "2008-11-20T13:53:20Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![johnnybutler7](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/8491ac/32.png) [@johnnybutler7](https://www.ruby-forum.com/u/johnnybutler7)\ **Post date:** [November 20, 2008, 1:53pm UTC](https://www.ruby-forum.com/t/search-reg-exp-for-exact-match/153722/1 "2008-11-20T13:53:20Z")
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? Jb ---
**Author:** ![johnnybutler7](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/8491ac/32.png) [@johnnybutler7](https://www.ruby-forum.com/u/johnnybutler7)\ **Post date:** [November 20, 2008, 2:21pm UTC](https://www.ruby-forum.com/t/search-reg-exp-for-exact-match/153722/2 "2008-11-20T14:21:31Z")
On Thu, Nov 20, 2008 at 1:49 PM, John B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > 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. ---
**Author:** ![johnnybutler7](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/8491ac/32.png) [@johnnybutler7](https://www.ruby-forum.com/u/johnnybutler7)\ **Post date:** [November 22, 2008, 11:55am UTC](https://www.ruby-forum.com/t/search-reg-exp-for-exact-match/153722/3 "2008-11-22T11:55:39Z")
On 20.11.2008 14:17, Jesús Gabriel y Galán wrote: > > “2010” =~ /\b2003|\2004|\2005|\2006|\2007|\2008|\2009\b/ > > 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 I’d rather use /\A200[3-9]\z/. > 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 Or irb(main):001:0\> s=“2005” =\> “2005” irb(main):002:0\> (2003…2009) === s[/\A\d{4}\z/].to\_i =\> true irb(main):003:0\> s=“2010” =\> “2010” irb(main):004:0\> (2003…2009) === s[/\A\d{4}\z/].to\_i =\> false irb(main):006:0\> (2003…2009).include? s[/\A\d{4}\z/].to\_i =\> false Note, this works because 0 (= nil.to\_i) is not part of the range! > If you have many numbers and many lookups, a Set should be better, > performance-wise. You can even use a bit set: irb(main):007:0\> t = (2003…2009).inject(0) {|mask,y| mask | 1 \<\< y} =\> 116650078639864259662055853239652489576667478532211432368528502061497852157464823887836603809757037023714110007321126217782227286423686421672874625786531963635756068971637276480699799614611885589371789821904502024698121311064730577770474098457113815634439476503092997189887743679313284635928742849521858004245675611528209841692017556564840683843349732924435866760173931843810360262352061792429448169450281904579322760817054128336138506834410834183565543664844525391283837108127106791786643268532096672079466512393065631776802367002142967381057920196424747178242497261636008255151052901022379808767413846016 irb(main):008:0\> t[s.to\_i] =\> 0 irb(main):009:0\> s=“2005” =\> “2005” irb(main):010:0\> t[s.to\_i] =\> 1 irb(main):011:0\> There are many ways… 🙂 > Now, if we are talking about ranges of years we can do even better: … or use the range test (as above) directly. Kind regards robert