15. help

Linux has some great built-in tools to help you how to use a command or check what flags are available for a command. One tool, help, is a built-in bash command that provides help for other bash commands (echo, logout, pwd, etc).

$ help echo

This will give you a description and the options you can use when you want to run echo. For other executable programs, it’s convention to have an option called --help or something similar.

$ echo --help

Not all developers who ship out executables will conform to this standard, but it’s probably your best shot to find some help on a program.