Basic regular expressions:
^ What begins with ^ m
To what end $ m $, also said blank lines or spaces, with a cat -An try
^ $ Symbols are not any blank lines
. Represents any "character"
\ Escape character does not resolve the meaning of special symbols, \ n corresponding to the Enter key, \ t corresponding to the tab
* Indicates a character in a row before the emergence of more than 0 or 0 times
. * Means any character, including blank lines, or regular expression means all consecutive occurrences.
[] Within brackets once for each character.
[^] [^ Acb], represents exclude a, b, c
Extended regular expressions:
+ Represents a letter before one or more consecutive or 1
| Means "or" means
() Represents a reference to the entire back reference / post
{} {N, m} previous consecutive characters at least N times, up to m consecutive times