Why is this regex invalid?

Ruby
1

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

2

On Thu, 7 Dec 2006 07:38:10 +0900, Daniel F.
[email protected] 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

3

On 12/6/06, Daniel F. [email protected] 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

4

On 12/6/06, Daniel F. [email protected] 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])([^-+ ]+)(.)/

5

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

6

Christopher S. [email protected] 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.

7

Daniel F. wrote:

the 2nd valid.

Why is this?

Thanks,
Dan

Hi,

‘-’ shuld be escaped like this.
regex = /([0-9])([^+- ]+)(.)/

Jun

8

On Thu, 07 Dec 2006 01:24:30 +0100, David K. wrote:

Christopher S. [email protected] 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

9

/([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”, “”]