Question

I found this operator by chance:

ruby-1.9.2-p290 :028 > "abc" !=~ /abc/
 => true

what’s this? It’s behavior doesn’t look like “not match”.

Answer 1

That’s not one operator, that’s two operators written to look like one operator.

From the operator precedence table (highest to lowest):

[] []=
**
! ~ + - [unary]
[several more lines]
<=> == === != =~ !~

Also, the Regexp class has a unary ~ operator:

~ rxp → integer or nil
Match—Matches rxp against the contents of $_. Equivalent to rxp =~ $_.

So your expression is equivalent to:

"abc" != (/abc/ =~ $_)

And the Regexp#=~ operator (not the same as the more familiar String#=~) returns a number:

rxp =~ str → integer or nil
Match—Matches rxp against str.

So you get true as your final result because comparing a string to a number is false.

For example:

>> $_ = 'Where is pancakes house?'
=> "Where is pancakes house?"
>> 9 !=~ /pancakes/
=> false
>> ~ /pancakes/
=> 9