Regex substitution: getting half of the string

I got another question about regex. The requirement is quite easy:

Given a string that has length of a even number.

  • 12
  • 1234
  • 123456
  • 12345678
  • abcdef

Write a substition regex to get the first half of the string:

After substition:

  • 1
  • 12
  • 123
  • 1234
  • abc

I'm using pcre, it supports recursion and control verbs.

I tried something like this but it's not working :(

s/^(?=(.))(?:((?1))(?1))+$/$2/mg

Here's the test subject on regex101

Is it possible? How can I achieve this?



Read more here: https://stackoverflow.com/questions/66997731/regex-substitution-getting-half-of-the-string

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