Display helpful information about commands.
man [-k] [command]
help [-s] [command]
-s Short usage synopsis, restricts the information displayed.
-k Search by command description rather than command name.
intro An overview of basic commands
Internal means a command built into the shell, it&qt;&qt;s the shell that performs the action.
External means the shell will fork and execute an external program as a new subprocess. External commands are available when running any shell.
For example, the cd command is built-in. The ls command, is external.
The man command lists all the internal commands for bash under man bash