Tài liệu 16.4. Online Help doc

16.4. Online Help
Mac OS X comes with over 1,200 Unix programs like the ones described in this chapter.
How are you supposed to learn what they all do?
Fortunately, almost every Unix program comes with a help file. It may not appear within
an elegant, gradient-gray Leopard window—in fact, it's pretty darned plain— but it offers
much more material than the regular Mac Help Center.
These user-manual pages, or manpages, hold descriptions of virtually every command
and program available. Mac OS X, in fact, comes with manpages on almost 9,000
topics—over 30,000 printed pages' worth.
Alas, manpages rarely have the clarity of writing or the learner-focused approach in the
Mac Help Center. They're generally terse, just-the-facts descriptions. In fact, you'll
probably find yourself needing to reread certain sections again and again. The
information they contain, however, is invaluable to new and experienced Unix fans alike,
and the effort spent mining them is usually worthwhile.
16.4.1. Using man
To access the manpage for a given command, type man followed by the name of the
command you're researching. For example, to view the manpage for the ls command,
enter: man ls.

Tip: The -k option flag lets you search by keyword. For example, man -k appletalk
produces a list of all manpages that refer to AppleTalk, whereupon you can pick one of
the names in the list and man that page name.

Now the manual appears, one screen at a time, as shown in Figure 16-7
.
Figure 16-7. To move on to the next man screen, press the Space bar. To go back,
press the up arrow key or the B key. To close the manual and return to a prompt,
press Q. You can also search for a certain phrase by typing a / (to produce the "find
what?" prompt); thereafter, type n to find the next occurrence.

A typical manpage begins with these sections:
•
Name. The name and a brief definition of the command.
•
Synopsis. Presents the syntax of the command, including all possible options and
arguments, in a concise formula. For example, the synopsis for du (disk usage) is
as follows: du [-H | -L | -P] [-I mask] [-a | -s | -d depth] [- ] [-h | -k] [-x] [file
…].
That line shows all the flags available for the du command and how to use them.
Brackets ([ ]) surround the optional arguments. (All of the arguments for du are
optional.)
Vertical bars called pipes (|) indicate that you can use only one item (of the group
separated by pipes) at a time. For example, when choosing options to use with du,
you can use either -H, -L, or -P—not two or all three at once.
The word file in the synopsis means "type a pathname here." The ellipsis (…)
following it indicates that you're allowed to type more than one pathname.
•
Description. Explains in more detail what the command does and how it works.
Often, the description includes the complete list of that command's option flags.
For more information on using man, view its own manpage by entering—what else?—
man man.

Tip: The free program ManOpen, available for download at www.missingmanuals.com
,
is a Cocoa manual pages reader that provides a nice looking, easier-to-control window for
reading manpages.Or why not just use Dashboard? Download the *NIX Manual widget
(from this book's "Missing CD" page at www.missingmanuals.com
, for example). It
provides an equally attractive interface to the manpages.

16.4.2. Other Online Help
Sometimes Terminal shoves a little bit of user manual right under your nose—when it
thinks you're having trouble. For example, if you use the mkdir command without
specifying a pathname, mkdir interrupts the proceedings by displaying its own synopsis
as a friendly reminder (subtext: "Um, this is how you're supposed to use me"), like this:
usage: mkdir [-pv] [-m mode] directory…