# Bug is ruby regexp **URL:** \ **Category:** Ruby\ **Created:** [February 2, 2007, 4:55pm UTC](https://www.ruby-forum.com/t/bug-is-ruby-regexp/84232 "2007-02-02T16:55:49Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![nicken](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/d07c76/32.png) [@nicken](https://www.ruby-forum.com/u/nicken)\ **Post date:** [February 2, 2007, 4:55pm UTC](https://www.ruby-forum.com/t/bug-is-ruby-regexp/84232/1 "2007-02-02T16:55:49Z")
Hello, I spotted this problem in ruby’s regexp today: $ irb(main):001:0\> num = “10” =\> “10” irb(main):002:0\> if num =~ /[9-13]/ irb(main):003:1\> puts “hello” irb(main):004:1\> end SyntaxError: compile error (irb):2: invalid regular expression: /[9-13]/ from (irb):4 from :0 irb(main):005:0\> I have tested it in ruby 1.8 and 0.9. Anyone else spotted this? ---
**Author:** ![nicken](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/d07c76/32.png) [@nicken](https://www.ruby-forum.com/u/nicken)\ **Post date:** [February 2, 2007, 5:04pm UTC](https://www.ruby-forum.com/t/bug-is-ruby-regexp/84232/2 "2007-02-02T17:04:50Z")
On Feb 2, 2007, at 9:54 AM, Nick B. wrote: > (irb):2: invalid regular expression: /[9-13]/ > from (irb):4 > from :0 > irb(main):005:0\> > > I have tested it in ruby 1.8 and 0.9. > > Anyone else spotted this? A character class ([…]) with a range of 9-1 is not valid in a regular expression because 1 does not come after 9 in your character encoding. I believe you were trying to verify that num is between 9 and 13. Your regex would not do this even if it was legal. Character classes give multiple choices for a single character, not a group of characters. Here are some ways to perform your check: > > num = “10” > > =\> “10” > > > num =~ /\A(?:9|1[0123])\Z/ > > =\> 0 > > > num.to\_i.between? 9, 13 > > =\> true Hope that helps. James Edward G. II ---
**Author:** ![nicken](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/d07c76/32.png) [@nicken](https://www.ruby-forum.com/u/nicken)\ **Post date:** [February 2, 2007, 5:29pm UTC](https://www.ruby-forum.com/t/bug-is-ruby-regexp/84232/3 "2007-02-02T17:29:51Z")
On Feb 2, 2007, at 11:03 AM, James Edward G. II wrote: > > irb(main):004:1\> end > > A character class ([…]) with a range of 9-1 is not valid in a > > > > > num = “10” > > > =\> “10” > > > num =~ /\A(?:9|1[0123])\Z/ > > > =\> 0 > > > num.to\_i.between? 9, 13 > > > =\> true > > Hope that helps. > > James Edward G. II or with a range: > > num = “10” > > =\> “10” > > (9…13) === num.to\_i > > =\> true > > num = “14” > > =\> “14” > > (9…13) === num.to\_i > > =\> false You could also have Float values > > num = “11.4” > > =\> “11.4” > > (9…13) === num.to\_i > > =\> true > > (9…13) === num.to\_f > > =\> true > > num = “13.1” > > =\> “13.1” > > (9…13) === num.to\_i > > =\> true > > (9…13) === num.to\_f > > =\> false Since num.to\_i is 13. -Rob Rob B. [http://agileconsultingllc.com](http://agileconsultingllc.com) removed\_email\_address@domain.invalid ---
**Author:** ![nicken](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/d07c76/32.png) [@nicken](https://www.ruby-forum.com/u/nicken)\ **Post date:** [February 2, 2007, 11:30pm UTC](https://www.ruby-forum.com/t/bug-is-ruby-regexp/84232/4 "2007-02-02T23:30:34Z")
On 2/2/07, James Edward G. II [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > encoding. > For comparative reference: $ perl -e ‘print “foo” if 9 =~ /[9-13]/’ Invalid [] range “9-1” in regex; marked by ← HERE in m/[9-1 ← HERE 3]/ at -e line 1. $ python -c “import re; re.match(‘[9-13]’, ‘9’)” Traceback (most recent call last): File “”, line 1, in ? File “/usr/lib/python2.4/sre.py”, line 129, in match return \_compile(pattern, flags).match(string) File “/usr/lib/python2.4/sre.py”, line 227, in \_compile raise error, v # invalid expression sre\_constants.error: bad character range ---
**Author:** ![nicken](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/d07c76/32.png) [@nicken](https://www.ruby-forum.com/u/nicken)\ **Post date:** [February 2, 2007, 11:39pm UTC](https://www.ruby-forum.com/t/bug-is-ruby-regexp/84232/5 "2007-02-02T23:39:35Z")
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**Author:** ![nicken](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/d07c76/32.png) [@nicken](https://www.ruby-forum.com/u/nicken)\ **Post date:** [February 3, 2007, 5:55am UTC](https://www.ruby-forum.com/t/bug-is-ruby-regexp/84232/6 "2007-02-03T05:55:59Z")
“Nick B.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes: > (irb):2: invalid regular expression: /[9-13]/ > from (irb):4 > from :0 > irb(main):005:0\> > > I have tested it in ruby 1.8 and 0.9. > > Anyone else spotted this? Its not a bug. The problem is you are mixing up characters and numbers. Regular expressions work on characters - they don’t know the number “13” only the characters 1 and 3. In your regexp, you have a character range of 9-1 and 3. However, 9 is greater than 1, so the range doesn’t make sense. Assuming you want to match on only the numbers 9, 10, 11, 12 and 13, you have two basic groupings - a single character ‘9’ or two characters in which the first is 1 and the second is in the range 0-3. A possible regexp could therefore be /^(?:9|1[0-3])$/ which says match “9” or “10” or “11” or “12” or “13”, but don’t put it into the match variables ((?:…). Note that you probably don’t need the ^ and $, but I always like to get into the habit of using them where possible as it anchors the regexp. If you don’t anchor a regexp, you can get really really bad performance due to loads of backtracking. However, this is more applicable when matching strings of text - with only a couple of characters, its not really and issue. I remember seeing a post to the perl group some years ago where someone was saying that using aregexp was causing their computer to hang. However, it turned out the problem was due to not anchoring the regexp. The computer wasn’t hung, it was just taking a long long time to perform the matching. As soon as the expression was anchored, the “hang” was eliminated. HTH Tim