UNIX Basics

The following is in part lifted from the tutorial in Chapter 2 of Glass.

Some UNIX philosophy

You will almost certainly find UNIX cryptic, using very short and often incomprehensible abbreviations for complicated commands. UNIX was developed as an environment/operating system for experienced programmers who were used to short abbreviations from working with assembly language, and who felt that short command sequences were preferable to more comprehensible but longer sequences. Unfortunately, this makes the learning curve very steep.

Some conventions

It is important to remember that UNIX is case-sensitive. That is, it will matter whether you type “echo”, or “ECHO”, or “Echo”, or “EcHo” --- all of these are different, and you must use the case indicated.

In these notes, I will use angle brackets --- < > --- in places where what I use is not what you should type, but a placeholder for what you should type, so, for example, < filename> stands for the name of the file you are interested in.

Getting started

Logging in

While the log-in process may possibly differ on different systems (particularly systems running UNIX lookalikes), and your first log-in may invoke some system bookkeeping, the basic process is the same:

You will see a prompt:

               login:

after which you should type your user name (note, do not retype the word “login”, as is required for the SHU network) and press Enter. You should then see the prompt:

               password:

You should type your password [Warning: it will not appear on the screen.] and then press Enter.

Thereafter, you will be in a shell, and you will see a prompt, such as $, # or > .

Shells and the kernel

The UNIX kernel provides the basic functionality of the operating system. However, most of the functionality we actually use is provided by a shell. There are several shells, of which the C- shell, the Bourne shell, and the Korn shell are common. Glass mostly uses the Korn shell, while I will stick mostly to the C-shell.

Many UNIX commands are really utilities provided by the shell, and many of these are common across all of the shells.

passwd

If this is your first log-on (or periodically on some systems), the system may ask you to change your password. You can also do this on your own. If the system is not leading you through the process, you can start the process by typing

               passwd

at the prompt. The system will then ask you to type your old password (to make sure you’re you), and then to type your new password twice (the second time basically to make sure you didn’t misspell the first time --- this could be disastrous).

Running a utility

At the prompt, type

    date

and press Enter.

The most useful commands in UNIX

The single most useful commands in UNIX invoke the help facility. However, the entire file will run through the screen without stopping. To make the file display one screen at a time, we will use more.

    more < filename>

will display the file one screen at a time. To see more screens of information, just press Space. To quit scrolling through the file, press q.

To view the results of another command with more, we “pipe” the results through more, as in DOS:

    man passwd | more.

There are basically two commands:

The man command takes the name of a command, and returns a description of the command.
- Type man passwd at the prompt. If the output takes more than one screen, repeat, typing

    man passwd | more

The apropos command (or the command man -k ) takes a term, and returns a list of the commands that have something to do with the term.
- Type apropos password | more at the prompt.

To save the results of a command in a file, we use a redirect character:

    man passwd >  passwd.out

will save the “man page” in a file passwd.out instead of displaying it on the screen. You can then display the file as often as you like using

    more passwd.out

Flags on commands

Most UNIX commands allow (and some require) options. Options are almost always specified with a minus sign followed by a symbol, possibly followed by text. For example, the man -k command above is the “apropos” option of the man command. For another example, lpr is the print command. To specify a given printer, use lpr -P< printer name> followed by a list of things to print. Other lpr flags control single-sided versus double-sided printing, number of copies to print, printing lengthwise or sideways, and so on.

Directories

Listing files
- Options on the ls command
Creating and removing directories
Changing directories
Specifying paths

Files

Creating files
Moving files around: mv, cp, rm
File protection: chmod, groups, chgrp, chown
Printing files: lpr, lpq, lprm

Miscellaneous

Mail

The mm mail server and its commands.
Mail configuration file.

Some Useful Utilities

clear will clear the screen. Some terminal emulators may leave garbage on the screen; this will eliminate it. Control-L may work in some cases.
wc < filename> will give the count of lines, words, and characters in < filename> .
file < filename> describes (the system’s best guess as to) the attributes of < filename> .

Logging Out

Type logout or exit. logout will log you out even if you are in a subshell; exit closes only the most recently opened foreground shell. Most UNIX users prefer using exit; otherwise, any pending work in open shells may be discarded. Control-D will work if ignoreof is not set.