Linux-shell-|, & {}, (), reg-command execution sequence

Linux-shell-|, & {}, (), reg-command execution sequence

 

&&
Format: command 1 & command 2
Purpose: & after the command on the left (command 1) returns true (that is, 0 is returned, successfully executed), the command on the right (command 2) can be executed.
Example:
$ MV/apps/bin/apps/dev/bin & Rm-r/apps/bin
Note: The/apps/bin directory will be moved to the/apps/dev/bin directory. If it is not successfully executed, the/apps/bin directory will not be deleted.

|
Format: command 1 | command 2
Purpose: if | the command on the left (command 1) is not executed successfully, execute | the command on the right (command 2)
For example, if the script is not successfully executed, the s h e l will end.
$ Comet month_end.txt | exit

Use () and {} to combine commands
How to execute multiple commands together:
1) execute a group of commands in the current shell. Each command can be separated by a command separator and all commands are enclosed in parentheses.
Format:
(Command 1; command 2 ;...)

2) subshell execution, replace () {}
Format: {command 1; command 2 ;...}

Note: Only when the output of all commands in {} is redirected as a whole, the commands are put into the sub-shell for execution. Otherwise, the commands are executed in the current S H E L

Comprehensive
These commands are used in combination.
Example:
$ Comet month_end | (echo "Hello, comet did not work" | mail myself; Exit)
If the script fails to be executed, first send an email to yourself and then exit.

(),{}

(Cmd1; cmd2;...; cmdn) # execute a group of commands in a sub-shell
{Cmd1; cmd2;...; cmdn} # execute a group of commands in the Current Shell

Regular Expression

^ Match only the beginning of a row
$ Only matches the end of a row
* Only one single character followed by *, matching 0 or more single characters
[] Only matches the characters in. It can be a single character or a character sequence. You can use-to represent the range of character sequences in []. For example, use [1-5] instead of [1 2 3 4 5].
\ Is used only to block the special meaning of a metacharacter. Because sometimes some metacharacters in s h e l have special meanings. \ Can make it meaningless
. Only match any single character
Pattern \ {n \} is only used to match the occurrence times of the previous pattern. N is the number of times
Pattern \ {n, \} m only indicates the same as above, but the minimum number of times is n
Pattern \ {n, m \} only indicates the same as above, but the occurrence frequency of pattern is between N and M.