Unix is a Four Letter Word: Unix --> Overview

Unix --> Overview

Case sensitivity

Unix is case sensitive. This means that Unix distinguishes between uppercase and lowercase letters, i.e. Biff and biff don't mean the same thing to Unix.

The shell

There are a number of different "flavors" of Unix available today. By different "flavors" I mean different command interpreters (called shells) which handle your input in their own unique way. This manual covers the C shell only. Many of the things found here will be identical with other shells, but don't count on it. It is possible to determine which shell is in use by typing echo $SHELL. The response for the C shell is /bin/csh which is what you should get. One other popular shell is the Bourne shell which would respond with /bin/sh.

Command syntax

Unix commands begin with a command name, often followed by flags and arguments some of which are optional. The generic syntax is:


    command [flags] argument1 argument2 ...

Normally the flags are preceded by a hyphen to prevent them from being interpreted as a filename. For example, in the command line


    ls -l avhrr

ls is the program called, -l is the flag, and avhrr is the argument. This command tells the computer to list (in long format) the file called avhrr or, if avhrr is a directory, to list all the files in the directory avhrr.

Correcting typos

There are three tools to destroy typos that occur on the command line. ¹


    <DEL>       Erases the previous character.
    <ctrl-W>    Erases the previous word.
    <ctrl-U>    Erases the whole command line.

Controlling your terminal output

If output scrolls up on your terminal screen faster than you can read it, you can suspend it by typing <ctrl-S>. To resume the display, type <ctrl-Q>. The Paging section will discuss how to pass output through a paging program that will automatically display only one screen at a time. While I'm at it, <ctrl-C> will abort a process, and <ctrl-O> will discard the output until another <ctrl-O> is entered. Be sure to note that although the output doesn't appear, the process is still running. <ctrl-Z> suspends the current program. You can see its job number by typing jobs. You can resume the suspended program by giving the fg (foreground) command, or resume it in the background with bg.

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¹ A couple of notes on notation here. The delete key varies from keyboard to keyboard. Your delete key may be labeled DEL, DELETE, BACKSPACE, RUB, or RUBOUT. Also, <ctrl-W> means holding down the <ctrl> key and pressing W. Control <ctrl> character commands are not case sensitive, i.e. <ctrl-w> is equivalent to <ctrl-W>.

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