Programming commands for Shell scripts

1:test variable-get 80 to determine whether it is greater than [] =test

2: Use the regular expression to use [[]]

3: [[]] = = Same, string do not add "" to this wildcard character

=~ match, string do not add "", support extended regular expression

4:read reads the contents of the keyboard input assign one or more shell variables

Read-s Mate password for password-n 3 limit user input character length

-T 3 limit time, 3 second break

5:$-variable set+h close variable

6:export from local changes to environment variables

7: (()) used to assign values can be the most basic additive subtraction, let can also

8: XOR: The same as 0, the difference is 1 with or: The same is 1, the difference is 0

9:true 1 True false 0 false! Take counter

10:&& Short Circuit with example: CMD1 && cmd2 execute Command 2 When command 1 succeeds, command 2 does not execute if command 1 fails

11:| | Short Circuit or example: cmd1 && cmd2 Command 1 succeeded if Command 2 was not executed, command 1 failed, command 2 executed

Programming commands for Shell scripts