valid Symbol literal characters in Ruby

gistfile1.txt

$ ruby -v
ruby 1.9.2p136 (2010-12-25)

$ ruby symbol_literals.rb
valid as first char:
@$_ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz
valid as middle char:
_ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789
valid as end char:
!_=?ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789

symbol_literals.rb

def symbol_chars_are_valid(symbol_chars)
  # :aaa == :"aaa" if it has valid Symbol literal chars
  eval ":#{symbol_chars} == :#{symbol_chars.inspect}"
rescue Exception
  false
end

chars_to_try =
  '`~!@$%^&*()-_+={}[]|\;:"<>,.?/'.split('') + ["'"] +
  ('A'..'Z').to_a + ('a'..'z').to_a + ('0'..'9').to_a

puts "valid as first char:"
puts chars_to_try.select {|c| symbol_chars_are_valid "#{c}aa" }.join ''
puts "valid as middle char:"
puts chars_to_try.select {|c| symbol_chars_are_valid "a#{c}a" }.join ''
puts "valid as end char:"
puts chars_to_try.select {|c| symbol_chars_are_valid "aa#{c}" }.join ''

pretty much the rule is: A non quoted symbol must make sense in ruby without the colon character (with a few exceptions). If it doesn't you can't use it.
So any identifier for constants (class, module), methods, variables (local, instance, class, global) can be a symbol

don't forget valid single character symbols

puts chars_to_try.select {|c| symbol_chars_are_valid "#{c}" }.join ''
`~!%^&*-_+|<>/ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz

What about these symbols?

:**
:>=
:[]
:[]=

You could also just escape the ' symbol like so:

`~!@$%^&*()-_+={}[]|\;:"<>\',.?/