The Linux command-line can appear pretty complicated and occasionally even a little alarming. But it also offers a whole stack of helpful documentation which you can access directly from the command-line. Read on to learn how to help yourself when – or even before – you get stuck.
A question you may have quite early on in your command-line exploration is: is there a command that does the thing I want to do? apropos is here to help. Manual pages (I'll discuss these in more detail below) are available for almost all Linux commands, and include a short description of the command. apropos searches this for the string you provide. So
apropos datewill output every command that has the word "date" in its name or its short description, as in this Figure 1.
This is helpful if you know that there is a command a bit like [whatever] but can't quite remember it; or if you're looking for a command to do a particular task. If you find a command that might be what you're after, but you're not sure, try checking its manual page (see next page).
If you know what command you want to use, and you know roughly how it works, but you've forgotten the details, then the option --help may be useful. For example, try the command:
du --helpto get information on what options you can use with the du command (this gives you information about disk usage). In some cases the help output may be too long for the screen: in this case try:
du --help | moreand press the space key to scroll down through the information.