Regexp ambiguity/error

[Ammar Ali]

Hello,

This is definitely an edge case, but an interesting one. Suppose we
have a configuration string like "muxff mixn" and we want to match
the "mixn" (actually either) part passively (i.e. not captured).

=> 4

Oops, forgot about options. 100% understandable.


Several attempts to work around it

Wrap one of the option characters in a set

"muxn mixff" =~ /\b(?[m]ixon|off))\b/

SyntaxError: (irb):2: undefined group option: /\b(?[m]ixon|off))\b/
from /Users/ammar/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in `<main>'

Wrap all option characters in individual sets

"muxn mixff" =~ /\b(?[m][x]on|off))\b/

SyntaxError: (irb):3: undefined group option: /\b(?[m][x]on|off))\b/
from /Users/ammar/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in `<main>'

Wrap the option characters in a group
SyntaxError: (irb):4: undefined group option: /\b(?(mix)on|off))\b/
from /Users/ammar/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in `<main>'

Move the anchors inside the passive group

"muxn mixff" =~ /(?\b(([m]ix)on|off))\b)/

SyntaxError: (irb):5: undefined group option: /(?\b(([m]ix)on|off))\b)/
from /Users/ammar/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in `<main>'


If the passivity is dropped, it works as intended, of course.
=> 7

The same occurs with ruby 1.8, but with a slightly different error message:

undefined (?...) sequence:

I was hoping that one of the workarounds above would work, but now I'm
thinking this is might be a bug. I want to see what others think
before I cry wolf.

Regards,
Ammar

 

[Ammar Ali]

My bad, again. I missed the ':' in all of those attempts.

Sorry about the noise.

Regards,
Ammar

Hello,

This is definitely an edge case, but an interesting one. Suppose we
have a configuration string like "muxff mixn" and we want to match
the "mixn" (actually either) part passively (i.e. not captured).

=3D> 4

Oops, forgot about options. 100% understandable.


Several attempts to work around it

Wrap one of the option characters in a set

"muxn mixff" =3D~ /\b(?[m]ixon|off))\b/

SyntaxError: (irb):2: undefined group option: /\b(?[m]ixon|off))\b/
=C2=A0 =C2=A0 =C2=A0 =C2=A0from /Users/ammar/.rvm/rubies/ruby-1.9.2-p0/bi=

Wrap all option characters in individual sets

"muxn mixff" =3D~ /\b(?[m][x]on|off))\b/

SyntaxError: (irb):3: undefined group option: /\b(?[m][x]on|off))\b/
=C2=A0 =C2=A0 =C2=A0 =C2=A0from /Users/ammar/.rvm/rubies/ruby-1.9.2-p0/bi=

Wrap the option characters in a group

SyntaxError: (irb):4: undefined group option: /\b(?(mix)on|off))\b/
=C2=A0 =C2=A0 =C2=A0 =C2=A0from /Users/ammar/.rvm/rubies/ruby-1.9.2-p0/bi=

Move the anchors inside the passive group

"muxn mixff" =3D~ /(?\b(([m]ix)on|off))\b)/

SyntaxError: (irb):5: undefined group option: /(?\b(([m]ix)on|off))\b)/
=C2=A0 =C2=A0 =C2=A0 =C2=A0from /Users/ammar/.rvm/rubies/ruby-1.9.2-p0/bi=