Now that you’re almost to the end of this guide, let’s look at some ways to continue learning about Unix. Documentation is an obvious choice, but it isn’t always in obvious places. You can save time by taking advantage of other shell features—aliases, functions, and scripts—that let you shorten a repetitive job and “let the computer do the dirty work.”
We’ll close by seeing how you can use Unix commands on non-Unix systems.
You might want to know the options to the programs we’ve introduced—and get more information about them and the many other Unix programs. You’re now ready to consult your system’s documentation and other resources.
Different versions of Unix have adapted Unix documentation in different ways. Almost all Unix systems have documentation derived from a manual originally called the Unix Programmer’s Manual. The manual has numbered sections; each section is a collection of manual pages, often called “manpages”; each program has its own manpage. Section 1 has manpages for general Unix programs such as who and ls.
Many Unix installations have individual manual pages stored on the computer; users can read them online. If your system has online manpages, and you want to know the correct syntax for entering a command or the particular features of a program, enter the command man and the name of the command. The syntax is:
man command
For example, if you want to find information about the program mail, which allows you to send messages to other users, enter:
$ man mail
.
.
$
The output of man may be filtered through a pager like less automatically. If it isn’t, just pipe the output of man to less (or more or pg).
After you enter the command, the screen fills with text. Press SPACE or RETURN to read more, and q to quit.
Some systems also have a command called apropos or man -k to help you locate a command if you have an idea of what it does but are not sure of its correct name. Enter apropos followed by a descriptive word; you’ll get a list of commands that might help.
Some commands—cd and jobs, for example—aren’t separate Unix programs; they’re part of the shell. On some Unix systems, you’ll find documentation for those commands in the manual page for the shell. (To find the shell’s name, see Section 1.1.3 in Chapter 1.)
If the program isn’t a standard part of your Unix system—that is, your system staff added the program to your system—there may not be a manual page, or you may have to configure the man program to find the local manpage files.
Linux systems, as well as some others, have a program called info. It serves the same purpose as man: to document system programs. The info output is in a different format, though. The syntax to start info is:
info command
For example, if you want to find information about the program find, which searches for files, enter info find. After you enter the command, press SPACE to read more or “q” to quit.
The Internet changes so quickly that any list of online Unix documentation we’d give you would soon be out of date. Still, the Internet is a great place to find out about Unix systems. Remember that there are many different versions of Unix—so some documentation you find may not be completely right for you. Also, some information you’ll find may be far too technical for your needs (many computer professionals use and discuss Unix). But don’t be discouraged! Once you’ve found a site with the general kind of information you need, you can probably come back later for more.
Many Unix command names are plain English words, which can make searching hard. If you’re looking for collections of Unix information, try searching for the Unix program named grep. As this book went to press, one especially Unix-friendly search engine was Google, at http://www.google.com.
Here are some other places to try:
Magazines, both in print and online-only, have Unix tutorials and links to more information. Many are written for beginners.
Publishers, like O’Reilly & Associates, Inc. (http://www.oreilly.com), have areas of their websites that feature Unix and have articles written by their books’ authors. They may also have books online (such as the O’Reilly Safari service) available for a small monthly fee—which is a good way to learn a lot quickly without needing to buy a paper copy of a huge book, most of which you may not need.
Vendors’ sites like Red Hat (http://www.redhat.com), and Unix-related organizations like the Free Software Foundation (http://www.fsf.org), usually have documentation and support files online, where you can search for what you need.
Universities often use Unix-like systems and will have online documentation. You’ll probably have better luck at the Computer Services division (which services the whole campus) than at the Computer Science department (which may be more technical).
Bookstores, both traditional and online, are full of computer books. The books are written for a wide variety of needs and backgrounds. Unfortunately, many books are rushed to press, written by authors with minimal Unix experience, full of errors. Before you buy a book, read through parts of it. Does the style (brief or lots of detail, chatty and friendly or organized as a reference) fit your needs? Search the Internet for reviews; online bookstores may have readers’ comments on file.
If you type command names that are hard for you to remember, or command lines that seem too long, you’ll want to learn about shell aliases and shell functions. These shell features let you abbreviate commands, command lines, and long series of commands. In most cases, you can replace them with a single word or a word and a few arguments. For example, one of the long pipelines Section 5.2 (Chapter 5) could be replaced by an alias or function named (for instance) “aug.” When you type aug at a shell prompt, the shell would list files modified in August, sorted by size.
Making an alias or function is almost as simple as typing in the command line or lines that you want to run. References in Section 8.1, earlier in this chapter, have more information. Shell aliases and functions are actually a simple case of shell programming.
We mention earlier that the shell is the system’s command interpreter. It reads each command line you enter at your terminal and performs the operation that you call for. Your shell is chosen when your account is set up.
The shell is just an ordinary program that can be called by a Unix command. However, it contains some features (such as variables, control structures, and so on) that make it similar to a programming language. You can save a series of shell commands in a file, called a shell script, to accomplish specialized functions.
Programming the shell should be attempted only when you are reasonably confident of your ability to use Unix commands. Unix is quite a powerful tool and its capabilities become more apparent when you try your hand at shell programming.
Take time to learn the basics. Then, when you’re faced with a new task, take time to browse through references to find programs or options that will help you get the job done more easily. Once you’ve done that, learn how to build shell scripts so that you never have to type a complicated command sequence more than once.
You might also want to learn Perl. Like the shell, Perl interprets script files full of commands. But Perl has a steeper learning curve than the shell. Also, since you’ve already learned a fair amount about the shell and Unix commands by reading this book, you’re almost ready to start writing shell scripts now; on the other hand, Perl will take longer to learn. But if you have sophisticated needs, learning Perl is another way to use even more of the power of your Unix system.
Once you get comfortable working quickly at the Unix command line, you may miss that power and flexibility when you use another system like Microsoft Windows. You can get programs—both commercial and freely available—that let you use a Unix-like shell prompt and Unix utilities (grep, sort, and so on) from within other operating systems. You’ll also find that an increasing number of systems are built on top of the stable Unix or a Unix-like operating system. Two of the latest examples are Mac OS X on the Macintosh and a variety of machines with Linux embedded inside.
Unix, Microsoft Windows, and the Macintosh all use different conventions for the way that they mark the end of a line of text. If you transfer text files between these systems, you’ll probably need to convert them. (The command-line FTP client does this automatically if you set its ascii transfer mode.) And if you have an executable program file that runs on one system, it won’t run on the others—unless it’s written in Java or it’s a script program from a language such as the shell or Perl.
Cygwin, from http://www.cygwin.com, is a package of Unix-like software development utilities that runs under Microsoft Windows NT, 98, and 95 (and probably others, as Microsoft Windows evolves). Although it’s aimed at software developers, it also has a lot of the standard Unix utilities. You can use Cygwin from its bash shell (a Unix-like shell) or from the standard Windows command shell.
The MKS Toolkit, from http://www.mks.com, is a commercial package of Unix-like utilities that runs under Microsoft Windows. MKS Toolkit has been on the market, and been updated constantly, since the time of MS-DOS in the 1980s.
With a little hunting, you’ll find versions of other Unix programs for Windows systems. Three of these are the Pine email program, the Lynx browser, and vim, a version of the vi text editor.
The latest version of the Macintosh operating system (as of this writing) is Mac OS X, a Unix-based system. The OS X window system, Aqua, interacts with the operating system much as the X Window System you’ve seen in this book. (In fact, you now can use X on the Mac!)
If you want to use a Unix-like terminal under OS X, you can open Terminal. It’s a regular double-clickable application found in /Applications/Utilities. Navigate to it using the Finder, launch it, and you’ll get a terminal window like the ones shown in this book.
Once you open Terminal, you can use standard Unix utilities on your Mac
files, on files you create with those utilities, or on files you
transfer over a network.
File pathnames are separated by slashes (/), just as
on Unix, but be sure to put quotes around Mac filenames that don’t follow
our file naming rules
(see Section 4.1 in Chapter 4).
Unlike Unix and Windows, some Macintosh files have two
forks: the resource and data forks.
If you copy a Mac file, watch out—the cp utility won’t copy both forks!
Instead, you’ll need to install and run
CpMac (from the
Developer Tools CD that comes with OS X; then you can simply run
/Developer/Tools/CpMac).