history:tldr:413a4

The command history ${20} is a command used in Unix-like operating systems, such as Linux, to display the last 20 executed commands from the command-line history.

Here's how the command works:

1. history: The history command is used to display the command-line history, which shows previously executed commands.
2. ${20}: This is a parameter used to specify the number of commands to display from the history. In this case, the number 20 indicates that the last 20 commands should be shown.

So, when you execute the command history ${20}, the system will retrieve and display the last 20 commands entered in the command line history.