grep command with regular expression (filter) three

Grep-e =egrep

+ one or more characters preceding the plus sign

[Email protected] ~]# egrep--color ' R+o ' 1.txtroot:x:0:0:root:/root:/bin/bashdrooaemon:x:2:2:daemon:/sbin:/sbin/ Nologinoperator:x:11:0:operator:/root:/sbin/nologin

. Represents any one character

* Represents 0 or more * preceding characters

. * Any of any characters

？ 0 or 1? The preceding character

+ 1 or more + preceding characters

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grep command with regular expression (filter) three