Shell (6)-command execution sequence

1. Run the &: & command on the left (command 1) To return the true result (0 is returned, and the result is successfully executed), and run the & command on the right (command 2) can be executed;

2. Run |: if | the command on the left (command 1) is not executed successfully, run | command on the right (command 2); 3. Run () and {} combine commands: In order to execute a group of commands in the current s h e l, you can use the command separator to separate each command, and enclose all commands in parentheses. If {} is used to replace (), the corresponding command will be executed as a whole in the child s h e l instead of the current s h e l, only when the output of all commands in {} is redirected as a whole, the commands are placed in the sub-s h e l for execution, otherwise, it is executed in the current s h e l.