regex - Why does Ruby /[[:punct:]]/ miss some punctuation characters?

Question

Ruby /[[:punct:]]/ is supposed to match all "punctuation characters". According to Wikipedia, this means /[][!"#$%&'()*+,./:;<=>?@^_`{|}~-]/ per POSIX standard.

It matches: -[];',./!@#%&*()_{}::"?.

However, it does not match: =`~$^+|<> (at least in ruby 1.9.3p194).

What gives?

Answer 1

The punctuation character class is defined by the locale. The Open Group LC_TYPE definition for punct says:

Define characters to be classified as punctuation characters. In the POSIX locale, neither the <space> nor any characters in classes alpha, digit, or cntrl shall be included. In a locale definition file, no character specified for the keywords upper, lower, alpha, digit, cntrl, xdigit, or as the shall be specified.

Basically, it defines how punct can be defined by exluding other character classes, but it doesn't actually define the punctuation symbols directly--that's the locale's job.

I couldn't find a canonical reference to what is in each locale. Maybe someone else knows. Meanwhile, you can find an LC_TYPE that matches the punct character class you want, or just specify the class directly.