Regular expressions in Linux sed commands need to be escaped with question marks, plus signs, parentheses, etc.

The regular expression syntax within the Linux SED command is divided into two types, one called Basic (BRE) Syntax and the other called Extended (ERE) Syntax. The BRE is used by default.

This bre is a simplified version, the syntax is slightly different, the question mark, plus, parenthesis, curly braces and vertical lines have no special meaning, that is, the character itself, if you want to define the implementation of special meaning, you need to use a backslash (\) escape ... For details, please see:

Https://www.gnu.org/software/sed/manual/html_node/BRE-vs-ERE.html#BRE-vs-ERE

Regular expressions in Linux sed commands need to be escaped with question marks, plus signs, parentheses, etc.