The closest thing I know of to this is https://github.com/devongovett/regexgen https://github.com/devongovett/regexgen (or my Ruby port https://github.com/amake

The closest thing I know of to this is https://github.com/devongovett/regexgen https://github.com/devongovett/regexgen (or my Ruby port https://github.com/amake/regexgen-ruby https://github.com/amake/regexgen-ruby). % bundle exec bin/regexgen '14:51 [info] 51 some message' '15:22 [error] 24 error!' (?-mix:1(?:4:51\ \[info\]\ 51\ some\ message|5:22\ \[error\]\ 24\ error!)) With enough inputs it should end up with something somewhat reasonable for the leading part, but it will never be smart enough to understand that the error message is "arbitrary" and should be matched with e.g. `(.+)`.