Question

I am using Ruby 1.9.3. I was playing with some patterns and found something interesting:

Example 1:

irb(main):001:0> /hay/ =~  'haystack'
=> 0
irb(main):003:0> /st/ =~ 'haystack'
=> 3

Example 2:

irb(main):002:0> /hay/.match('haystack')
=> #<MatchData "hay">
irb(main):004:0> /st/.match('haystack')
=> #<MatchData "st">

=~ returns the first location of its first match, whereas match returns the pattern. Other than that, is there any difference between =~ and match()?

Execution time difference (As per @Casper)

irb(main):005:0> quickbm(10000000) { "foobar" =~ /foo/ }
Rehearsal ------------------------------------
   8.530000   0.000000   8.530000 (  8.528367)
--------------------------- total: 8.530000sec

       user     system      total        real
   8.450000   0.000000   8.450000 (  8.451939)
=> nil

irb(main):006:0> quickbm(10000000) { "foobar".match(/foo/) }
Rehearsal ------------------------------------
  15.360000   0.000000  15.360000 ( 15.363360)
-------------------------- total: 15.360000sec

       user     system      total        real
  15.240000   0.010000  15.250000 ( 15.250471)
=> nil

Answer 1

First make sure you’re using the correct operator: =~ is correct, ~= is not.

The operator =~ returns the index of the first match (nil if no match) and stores the MatchData in the global variable $~. Named capture groups are assigned to a hash on $~, and, when the RegExp is a literal on the left side of the operator, are also assigned to local variables with those names.

>> str = "Here is a string"
>> re = /(?<vowel>[aeiou])/    # Contains capture group named "vowel"
>> str =~ re
=> 1
>> $~
=> #<MatchData "e" vowel:"e">
>> $~[:vowel]    # Accessible using symbol...
=> "e"
>> $~["vowel"]    # ...or string
=> "e"
>> /(?<s_word>\ss\w*)/ =~ str
=> 9
>> s_word # This was assigned to a local variable
=> " string"

The method match returns the MatchData itself (again, nil if no match). Named capture groups in this case, on either side of the method call, are assigned to a hash on the returned MatchData.

>> m = str.match re
=> #<MatchData "e" vowel:"e">
>> m[:vowel]
=> "e"

See http://www.ruby-doc.org/core-1.9.3/Regexp.html (as well as the sections on MatchData and String) for more details.