Match part of a regular expression back reference

Question

I want to write a regular expression that will match a pattern that repeats at least twice, followed by part of the same pattern.

For example, abcabca should match, as should abcabcab, defdefdefde, etcetera.

I think I need to use back references for this. I envision something like ^(.+?){2,}\1$ but somehow matching only part of the \1 back reference.

Given the repeating pattern abc, I want to match at least 2 occurrences of abc, followed by part of the string abc.

These should match:

• FooFooF (This is 2 repeats of Foo followed by the first letter in Foo)
• FooFooFoo (This is either 3 repeats of Foo, followed by a 0-length substring or 2 followed by the entire word as a substring. It depends on how you look at it.)
• FooFooFooFo (This is 3 repeats followed by Fo, the first two letters in Foo)

These shouldn't:

• Foo (There need to be 2+ repeats)
• FooFo (This is only 1 repeat)
• FooFooFoX (FoX is not part of the string Foo, so it doesn't match.)

Is this possible? If so, how can I do it?

Answer 1

If you want to fit a pattern for 3 character you can use a regex like this:

\b(.{3})\1.*?\b

Working demo

But if you want to have whatever pattern defined for the first characters then you could use:

\b(.+)\1.*?\b

Working demo