8.10 Shell special symbol cut command
- : Represents any number of arbitrary characters
? : Represents any single character
#: Represents the comment character
\ Represents the escape character
| Represents the pipe character The
cut command is used to intercept a field
-d specifies the delimiter, which is enclosed in double quotation marks (-d ":" specifies the colon delimiter )
-c: specify the first few characters
-f: which block is connected
8.11 sort_wc_uniq command The
sort command is mainly used for sorting
-t: add a delimiter (same as cut -d plus delimiter)
-n: means pure numeric sorting
-r: reverse sorting
-u: means deduplication
wc -l: command Indicates the number of statistical lines
uniq -c : the command indicates
8.12 tee_tr_split command 
tr command: replace character tr [az] [AZ] to lowercase to uppercase 
8.13
$ variable prefix under shell special symbols, ! $ , which indicates the end of the line
; multi-line commands are written on one line, separated by a semicolon
~ user home directory, and the following regular expression indicates that the matching character
& is placed after the command, and the command will be thrown into the background
[0-9] [az ][AZ][abcd] specifies one of the characters
|| and && are used between commands
