记不得，憋不住 | Can't Remember, Can't Shut Up

官方说明：   -E, -r, --regexp-extended                  use extended regular expressions in the script                  (for portability use POSIX -E). 详细解释 5.2 Basic (BRE) and extended (ERE) regular expression Basic and extended regular expressions are two variations on the syntax of the specified pattern. Basic Regular Expression (BRE) syntax is the default in  sed  (and similarly in  grep ). Use the POSIX-specified  -E  option ( -r ,  --regexp-extended ) to enable Extended Regular Expression (ERE) syntax. In GNU  sed , the only difference between basic and extended regular expressions is in the behavior of a few special characters: ‘ ? ’, ‘ + ’, parentheses, braces (‘ {} ’), and ‘ | ’. With basic (BRE) syntax, these characters do not have special meaning unless prefixed with a backslash (‘ \ ’); While with extended (ERE) syntax it is reversed: these characters ...