Question

I have a check of the following type

 validates :callback_handle, :format => { :with => /[_0-9a-zA-Z]+/ix }, :unless  => "callback.nil?"

I do not want any non 0-9, a-z A-Z characters to pass. So i set callback_handle to
“!alksjda” (note ! at the begining).
This test does not fail. What am I doing wrong?

I tried a few things on irb: This is what I got:

1.9.2-p320 :001 > a = "!askldjlad"
 => "!askldjlad" 
1.9.2-p320 :002 > a =~ /[_0-9a-zA-Z]+/ix
 => 1 
1.9.2-p320 :003 > a = "askldjlad"
 => "askldjlad" 
1.9.2-p320 :004 > a =~ /[_0-9a-zA-Z]+/ix
 => 0 

I thought it would return false or nil on failure to find the match.

Can someone tell me what is wrong here in my understanding?

EDIT:
I figured out that =~ will return position of a match.
So the question becomes How do I not allow something that has any other character to not match?

Answer 1

Your regular expression is still able to match, because there is at least 1 character in your string that is alpha-numeric. If you want to make sure that the entire string matches then you should define the beginning and end of the match.

Old:

a =~ /[_0-9a-zA-Z]+/ix

This is saying “match at least one of these characters somewhere in a.

New:

a =~ /\A[_0-9a-zA-Z]+\z/ix

This is saying “start at the beginning of the string, then match at least 1 of only these characters, followed by the end of the string” in a.