# Why is this regex invalid? **URL:** \ **Category:** Ruby\ **Created:** [December 6, 2006, 11:38pm UTC](https://www.ruby-forum.com/t/why-is-this-regex-invalid/78571 "2006-12-06T23:38:47Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![arachnd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/278dde/32.png) [@arachnd](https://www.ruby-forum.com/u/arachnd)\ **Post date:** [December 6, 2006, 11:38pm UTC](https://www.ruby-forum.com/t/why-is-this-regex-invalid/78571/1 "2006-12-06T23:38:47Z")
irb(main):002:0\> regex = /([0-9]_)([^±]+)(._)/ SyntaxError: compile error (irb):2: invalid regular expression: /([0-9]_)([^±]+)(._)/ from (irb):2 irb(main):003:0\> regex = /([0-9]_)([^+ -]+)(._)/ =\> /([0-9]_)([^+ -]+)(._)/ The only thing that it different in the 2 regexps is the placement of the space in the square brackets, yet the first regexp is invalid and the 2nd valid. Why is this? Thanks, Dan ---
**Author:** ![arachnd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/278dde/32.png) [@arachnd](https://www.ruby-forum.com/u/arachnd)\ **Post date:** [December 6, 2006, 11:44pm UTC](https://www.ruby-forum.com/t/why-is-this-regex-invalid/78571/2 "2006-12-06T23:44:48Z")
On Thu, 7 Dec 2006 07:38:10 +0900, Daniel F. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > the 2nd valid. > > Why is this? When an unescaped - appears in any position but the first or final one inside brackets, it is interpreted as a range separator rather than a literal ‘-’. Apparently '+- ’ isn’t a valid range. -mental ---
**Author:** ![arachnd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/278dde/32.png) [@arachnd](https://www.ruby-forum.com/u/arachnd)\ **Post date:** [December 6, 2006, 11:44pm UTC](https://www.ruby-forum.com/t/why-is-this-regex-invalid/78571/3 "2006-12-06T23:44:48Z")
On 12/6/06, Daniel F. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > the 2nd valid. > > Why is this? > > Thanks, > Dan It’s the placement of the - that makes a difference. In a character class, - between two characters denotes a range. So the first character class includes a range, from + to , which is invalid because + comes after space in the relevant character encoding. If you want a literal hyphen in a character class, it’s safest to make it the last character. -A ---
**Author:** ![arachnd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/278dde/32.png) [@arachnd](https://www.ruby-forum.com/u/arachnd)\ **Post date:** [December 6, 2006, 11:46pm UTC](https://www.ruby-forum.com/t/why-is-this-regex-invalid/78571/4 "2006-12-06T23:46:49Z")
On 12/6/06, Daniel F. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > the 2nd valid. The hyphen in the middle expression is ambiguous, because it could either be a range or a literal. One way is to rearrange the order so that it comes first: /([0-9]_)([^-+]+)(._)/ ---
**Author:** ![arachnd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/278dde/32.png) [@arachnd](https://www.ruby-forum.com/u/arachnd)\ **Post date:** [December 6, 2006, 11:46pm UTC](https://www.ruby-forum.com/t/why-is-this-regex-invalid/78571/5 "2006-12-06T23:46:49Z")
I’m pretty sure the dash needs to be escaped in regular expressions. The second one works since it is the last character in the character class, and hence isn’t defining a range. /([0-9]_)([^+-]+)(._)/ should work - note the escaped dash. -Chris Schneider ---
**Author:** ![arachnd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/278dde/32.png) [@arachnd](https://www.ruby-forum.com/u/arachnd)\ **Post date:** [December 7, 2006, 1:27am UTC](https://www.ruby-forum.com/t/why-is-this-regex-invalid/78571/6 "2006-12-07T01:27:01Z")
Christopher S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes: > I’m pretty sure the dash needs to be escaped in regular expressions. > The second one works since it is the last character in the character > class, and hence isn’t defining a range. > > /([0-9]_)([^+-]+)(._)/ should work - note the escaped dash. Rubbish. In character ranges, \ is not special. ---
**Author:** ![arachnd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/278dde/32.png) [@arachnd](https://www.ruby-forum.com/u/arachnd)\ **Post date:** [December 6, 2006, 11:48pm UTC](https://www.ruby-forum.com/t/why-is-this-regex-invalid/78571/7 "2006-12-06T23:48:50Z")
Daniel F. wrote: > the 2nd valid. > > Why is this? > > Thanks, > Dan Hi, ‘-’ shuld be escaped like this. regex = /([0-9]_)([^+-]+)(._)/ Jun ---
**Author:** ![arachnd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/278dde/32.png) [@arachnd](https://www.ruby-forum.com/u/arachnd)\ **Post date:** [December 7, 2006, 6:01am UTC](https://www.ruby-forum.com/t/why-is-this-regex-invalid/78571/8 "2006-12-07T06:01:27Z")
On Thu, 07 Dec 2006 01:24:30 +0100, David K. wrote: > Christopher S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes: > > > I’m pretty sure the dash needs to be escaped in regular expressions. > > The second one works since it is the last character in the character > > class, and hence isn’t defining a range. > > > > /([0-9]_)([^+-]+)(._)/ should work - note the escaped dash. > > Rubbish. In character ranges, \ is not special. It most certainly is special: irb(main):014:0\> /[a+-]/=~“.\” =\> nil ---
**Author:** ![arachnd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/278dde/32.png) [@arachnd](https://www.ruby-forum.com/u/arachnd)\ **Post date:** [December 7, 2006, 2:31am UTC](https://www.ruby-forum.com/t/why-is-this-regex-invalid/78571/9 "2006-12-07T02:31:07Z")
> > /([0-9]_)([^+-]+)(._)/ should work - note the escaped dash. > > Rubbish. In character ranges, \ is not special. A rubbish upon your rubbish. \ are special pretty much anywhere. Otherwise how would you match all chars except a ‘]’ ? irb(main):007:0\> /([0-9]_)([^±]+)(._)/.match(‘44dads’)[0…-1] =\> [“44dads”, “44”, “dads”, “”] irb(main):008:0\> /([0-9]_)([^±]+)(._)/.match(‘44-dads’)[0…-1] =\> [“44-dads”, “4”, “4”, “-dads”] irb(main):009:0\> /([0-9]_)([^±]+)(._)/.match(‘44-dads’)[0…-1] SyntaxError: compile error (irb):9: invalid regular expression: /([0-9]_)([^±]+)(._)/ from (irb):9 irb(main):010:0\> /([0-9]_)([^±]+)(._)/.match(‘44\dads’)[0…-1] =\> [“44\dads”, “44”, “\dads”, “”]