Here’s a breakdown of the man -k PostScript command line:
man. The command name, tells the computer to look at the manual pages. These provide documentation for commands. For example, man whoami will give you documentation on the whoami command.
-k. The option, changes the behavior of man. Normally man expects a command name, such as whoami, for an argument and looks for documentation of that command. But with the -k or -apropos option, it expects the argument to be a keyword. It then gives a list of all manual pages with that keyword in their description.
PostScript. is the argument; because we used the -k option, it’s the keyword to search for.
Go ahead and type man -k PostScript, and you will see a list of all the manual pages on your system that have something to do with PostScript. If you haven’t installed much software, you might see the message PostScript: nothing appropriate instead.
Note: You can skip this section if you want to move on.
There’s a traditional, concise way of describing command _syntax. Syntax_ means the correct ways to combine various options and arguments. For example, if you type man man to get the manual page about man, you’ll see several syntax descriptions beginning with the command name man. One of them will look like this: man -k [-M path] keyword ...
Anything in brackets ([]) is an optional unit. In this case you don’t have to use the -M option, but if you do, you must use a path argument. You must use the -k option and the keyword argument. The ... means that you could have more of whatever came before it, so you could look up several keywords.
Let’s look at one of the more complex descriptions from the man manual page:
man [-c|-w|-tZT device] [-adhu7V] [-m system[,...]] [-L locale] [-p string] [-M path] [-P pager] [-r prompt] [-S list] [-e extension] [[section] page ...] ...
There’s no need to go through all of this (and don’t worry about what it all means), but do pay attention to the organization of the description.
First, clusters of options usually mean you can use one or more of them in different combinations, so -adhu7V means you can also use -h. However, you can’t always use all combinations; this description doesn’t make that clear. For example, -h is incompatible with other options, but you could do man -du. Unfortunately, the description’s format does not make this clear.
