CMP0186
-------

.. versionadded:: 4.1

Regular expressions match ``^`` at most once in repeated searches.

This policy affects commands that perform multiple regular expression
searches:

* :command:`string(REGEX MATCHALL)`
* :command:`string(REGEX REPLACE)`
* :command:`list(TRANSFORM REPLACE)`

and the generator expression :genex:`$<LIST:TRANSFORM,list,REPLACE>`.

CMake 4.0 and below match the ``^`` anchor at the start of every
successive search, leading to multiple matches:

.. code-block:: cmake

  string(REGEX REPLACE "^a" "b" result "aaaa") # result="bbbb"
  string(REGEX MATCHALL "^a" result "aaaa")    # result="a;a;a;a"

CMake 4.1 and above prefer to match the ``^`` anchor at most once,
at the start of the input string:

.. code-block:: cmake

  string(REGEX REPLACE "^a" "b" result "aaaa") # result="abbb"
  string(REGEX MATCHALL "^a" result "aaaa")    # result="a"

This policy provides compatibility for projects that have not been updated.

The ``OLD`` behavior for this policy is to match ``^`` multiple times,
at the start of each search.  The ``NEW`` behavior for this policy is
to match ``^`` at most once, at the start of the input string.

.. |INTRODUCED_IN_CMAKE_VERSION| replace:: 4.1
.. |WARNS_OR_DOES_NOT_WARN| replace:: does *not* warn
.. include:: include/STANDARD_ADVICE.rst

.. include:: include/DEPRECATED.rst
