Regular expressions with sed command (draft)

Regular expressions
. Match any single character
* Match any number of individual characters before it (can be a regular expression, such as. * represents any length that matches any character)
^ The regular expression followed by the match, at the beginning of the row or string
$ matches the preceding regular expression, at the end of a string or line
[...] Any character within the matching square brackets ((-) refers to the range of contiguous characters, (^) is the inverse meaning)
\{n,m\} matches the number of times that a single character in front of it recurs. \{n\} refers to reproducing n times;
\{n,\} is reproduced at least n times, \{n,m\} is reproduced n to M times
\{\} stores the pattern between \ and \ in a special "Reserved Space" (up to 9). Storage mode can be used from \1 to \9
For example: \{ab\}.*\1 represents two times of the AB combination and can have any number of characters in the middle.
{n,m} As with \{n,m\}, ERE (extended regular expression)
+ Match one or more instances of the preceding regular expression ERE
? Match 0 or one instance of the preceding regular expression ERE
| A regular expression that matches the before or after of the | symbol ERE Fast|slow (can match the sequence)
() matches the regular expression group in square brackets ERE

\ (ab\) \ (cd\) [def]*\2\1
\ (why\). *\1
\ ([[: alpha:]_][[:alnum:]_]*\) = \1
\ ([' ']\ '). *\1

SED command

sed [option] ' command ' input_file

The usual option
-n lists only those rows that have been processed by SED
-E perform SED action editing directly in instruction-list mode
-F filename writes the action of SED directly in a file
-R enables SED to support extended regular expressions
-I directly modifies the contents of the read file instead of the screen output

Select the rows you want to work with
/pattern/a line that matches the PATTERN of regular expressions
1 or 2 ... $ indicates the number of lines, $ represents the last line
1,$ represents the first line to the last row

The following commands are commonly used (the corresponding lines should be checked before using the command):
A \ Adds a string after the currently selected row
Sed ' 1a \add one ' test.txt adds a line after the first line add one
Sed ' 1, $a \add One ' test.txt adds a line after all rows from the first line to the last row add one
Sed '/first/a \ Add one ' test.txt adds a row after the line containing first:

C \ Replace the currently selected row with a string
Sed ' $c \add One ' Test.txt replaces the last line with the string add one
Sed ' 4, $c \add One ' test.txt replace the contents of line fourth to the last line with add one
Sed '/^ha.*day$/c \add one ' test.txt will start with HA and replace the line ending with day with add one

D Delete the currently selected row

i \ Inserts a string before the currently selected line

P Print the currently selected line to the screen

S/pattern/string/[g|i] Replace PATTERN strings with string
Sed '/line/text/g ' replaces all lines with Test G (global) without G will only replace our first line
Sed ' s/\ (. *\) line$/\1/g ' Delete all lines at the end of line

Regular expression with sed command (draft)