Symbols in the shell (in construction ... ）

The difference between 1, ' and $ ()

The anti-quote itself escapes the \, retains its own meaning, and if we want to play a special meaning in the anti-quote, we have to use 2 \ to represent it. So we can simply imagine the inverted quote: \ \ = \

$ () does not need to consider the problem, as we normally use: \ = \

Digression: Anti-quotes are old usage, $ () is a new usage, whether in the learning test, or in the actual work, the use of $ () is recommended.

2. Eval command

3. crontab command

The function of the crontab command is to schedule execution of some commands at certain intervals.

We can add the command to execute with CRONTAB-E. The result of the command execution, either standard output or error output, is sent to the user in the form of a message.

Symbols in the shell (in construction ... ）