Question

Using ruby regexp I get the following results:

>> 'foobar'[/o+/]
=> "oo"
>> 'foobar'[/o*/]
=> ""

But:

>> 'foobar'[/fo+/]
=> "foo"
>> 'foobar'[/fo*/]
=> "foo"

The documentation says:
*: zero or more repetitions of the preceding
+: one or more repetitions of the preceding

So i expect that ‘foobar'[/o*/] returns the same result as ‘foobar'[/o+/]

Does anybody have an explanation for that

Answer 1

'foobar'[/o*/] is matching the zero os that appear before the f, at position 0
'foobar'[/o+/] can’t match there because there needs to be at least 1 o, so it instead matches all the os from position 1

Specifically, the matches you are seeing are

'foobar'[/o*/] => '<>foobar'
'foobar'[/o+/] => 'f<oo>bar'