# CMP0186

Added in version 4.1.

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

This policy affects commands that perform multiple regular expression searches:

- `string(REGEX MATCHALL)`

- `string(REGEX REPLACE)`

- `list(TRANSFORM REPLACE)`

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

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

    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:

    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.

This policy was introduced in CMake version 4.1. It may be set by `cmake_policy()` or `cmake_minimum_required()`. If it is not set, CMake does not warn, and uses `OLD` behavior.

Note

The `OLD` behavior of a policy is deprecated by definition and may be removed in a future version of CMake.