ERE
Extended Regular Expression
拡張した正規表現
対比して古い方をBREと呼ぶ
https://www.gnu.org/software/sed/manual/html_node/BRE-syntax.html
https://entree.hatenadiary.org/entry/20141126/1417016871
https://jmatsu.hatenablog.com/entry/2017/01/30/130952
https://hydrocul.github.io/wiki/commands/sed.html#extended-regexp