Unix Concepts Glossary

absolute path name

An absolute path name is the address of a file or directory, specified with the root directory as the starting point.

access mode

The access mode is the first column of an ls -l listing. The access mode is composed of a file type followed by the user permissions, group permissions, and other permissions.

access string

An access string is the symbolic argument used with the chmod command.

account

Your account (or user account) is a unique environment within a UNIX system. An account comes with a user ID and a home directory.

alias

An alias is a brief label that provides a command shortcut. For example, by defining an alias, you can execute a complex command by typing only a few characters of the alias.

anchor

An anchor is a metacharacter such as ^ or $ that restricts a match to a particular position.

Anonymous FTP

Anonymous FTP is a connection to a public FTP site without the use of an assigned user name and password. You enter the user name anonymous to sign on and your access is limited.

append redirection operator

Using the append redirection operator, >>, you can add output to the end of an existing file.

archive

An archive is a set of files that are packaged as a single, large file.

arguments

Command arguments are the files, directories, or other objects that a command acts on.

block

A block is a unit of storage equal to 512 bytes.

buffer

A buffer is an area of memory where data are temporarily stored.

case sensitive

When a text search is case sensitive, the search treats uppercase and lowercase letters differently. If uppercase and lowercase letters are treated the same way, then the search is considered to be case in-sensitive.

command history

Command history is a C shell feature that lets you display previously entered commands, rerun them, or run modified versions of them.

command interpreter

Command interpreter is another term for the UNIX shell, because it processes the commands you enter.

command mode

Command mode is one of two modes of operation in vi. In command mode, you can move the cursor and issue editing commands, but you must switch to text mode to add text.

command-line interface

A command-line interface is one way of interacting with UNIX, in which you type commands at a prompt and the shell interprets them.

configuration options

Configuration options control vi's behavior. Use the :set command to manage these options.

Ctrl-C

Pressing Ctrl-C interrupts a command and returns you to the shell prompt. Ctrl-C is executed by holding down the Control key (labeled Ctrl) and pressing the C key.

current directory

Your current location in the file system. By default, UNIX commands apply to the current directory.

cwd variable

The cwd variable is a C shell variable that stores the name of your current working directory.

default printer

When you don't specify a printer name with your print command, the print request is sent to your default printer. The system administrator defines your default printer for you.

directory

A directory contains files and other directories. A directory is like a folder on Macintosh or Windows.

directory tree

A directory tree is the set of all files and subdirectories organized under a particular directory.

disk usage

Disk usage is the amount of storage space your files occupy on the disk.

download

To download means to transfer data from a remote computer.

ex editor

ex is a line editor that serves as an underlying program for the vi editor. A line editor is a program in which you see only one line at a time.

extract

To extract files from an archive means to copy them out of an archive and onto the filesystem.

file

A file is the basic unit of storage on UNIX, just as on any operating system.

file compression

File compression is a way of packing a file's contents more efficiently, so that the file takes up less disk space.

file owner

The file owner is typically the user who created the file. You can change permissions only on files you own.

File Transfer Protocol

The File Transfer Protocol, or FTP, is the set of communication rules that computers use to exchange files.

file type

The file type is the first character in an access mode. The most common file types are - for a regular file and d for a directory.

filter

A filter can take input from another command, manipulate the data in some way, and produce output. Filters are regular UNIX commands. Examples include head, tail, more, pr, grep, and sort.

FTP

Abbreviation for File Transfer Protocol.

FTP session

When your computer connects to an FTP server, also called an FTP site, you are engaged in an FTP session.

group

A group allows an arbitrary set of users to share files. When a user is a member of the file's group, the user will have that file's group permissions.

group permissions

Group permissions are the second set of read/write/execute permissions in an access mode. Group permissions apply to users that are members of the file's group.

GUI

A GUI, short for graphical user interface, is a system of windows, menus, and icons that you can click and drag with a mouse. Operating systems such as Macintosh, Windows, and UNIX provide a GUI.

Hard link

A hard link is another name for a file.

hidden file

A hidden file starts with a dot (.) and is not seen unless you specify the -a option of ls. Hidden files usually contain preference settings that control your UNIX environment or the way certain commands behave.

hierarchical file system

A hierarchical file system is like an inverted tree. Files are organized in directories. Directories are contained in higher-level directories, and so on until you reach the top-level directory, called root.

history substitution

History substitution is one of the tasks you can perform using the command history feature. History substitution lets you replay all or part of a previous command.

history variable

The history variable is a C shell variable that stores the number of commands you want in your command history.

home directory

Your home directory is a unique place in the file system where you can store and create files.

input/output redirection

Input/output redirection is a feature that lets you change the normal location that UNIX reads input from or writes output to.

job control

Job control is a feature for managing multiple commands that are running. Job control lets you run a command behind the scenes, so you do not need to wait for the command to finish.

kernel

The kernel is the core of the UNIX operating system. The kernel remains hidden from typical users.

Keyboard macro

A keyboard macro lets you perform a sequence of vi commands as a single keystroke. Keyboard macros also are called keyboard maps because they are created using the :map command.

Korn shell

The Korn shell is a commonly used UNIX shell. It's a superset of the Bourne shell, and in the command line offers conveniences similar to those of the C shell.

line editor

A line editor is a primitive editing program in which you see only one line at a time. An example of a line editor is ex, the underlying program of vi.

link

A link is another name for a file. A link is similar to a Macintosh alias or a Windows shortcut.

local computer

In an FTP session, the local computer is the one from which you connect to an FTP server. The FTP server is the remote computer.

logging in

Logging in is the process of supplying your user ID and password to identify yourself to the system.

man page

A man page (short for manual page) is an online reference for a particular UNIX command.

metacharacter

A metacharacter is a character with special meaning in regular expressions and is not treated literally. Examples include the * and . metacharacters.

multiplier

In vi, a multiplier is a number that you place before a movement command or editing command to extend the range of the command.

multiuser operating system

A multiuser operating system allows more than one person to use it at a time. UNIX is a multiuser operating system. Macintosh and Windows 98 are single-user operating systems.

operating system

An operating system is a computer's main control program. It manages how the system works (for example, the terminals, printers, files on disk, and memory). UNIX, Macintosh, and Windows are examples of operating systems.

operator

In vi, an operator is one of the letters c, d, or y, which combine with a movement command to create an editing command.

options

Options modify the behavior of a command. Options (sometimes called flags or switches) are usually a single letter preceded by a minus (-) sign.

other permissions

Other permissions are the third set of read/write/execute permissions in an access mode. Other permissions apply to everyone besides the file owner and the group members.

output redirection operator

Using the output redirection operator, >, you can sent output to a file.

parent directory

Compared to your current directory, the parent directory is the one that is immediately higher in the hierarchy. To navigate to a parent directory, use the .. (dot dot) notation.

path name

A path name indicates the location of a file within the file system.

pattern matching

Pattern matching is the task of using regular expressions to search for text.

permission type

A permission type grants users a particular type of access. The three basic permission types are r (read), w (write), and x (execute).

pipe

A pipe is a technique for using the output from one command as the input of another command. To form a pipe, place the pipe character ( | ) between two commands.

porting

Porting software means adapting it to run on another type of machine. UNIX became popular because it's portable, meaning that it can run on different types of computers. Unfortunately, this also led to the creation of many different UNIX variants.

print queue

The print queue is the list of items waiting to be printed.

print request

A print request is generated whenever you issue a print command.

prompt

A prompt is a character (or a word or two) that is displayed whenever the shell or some other program is expecting you to type something. The C shell prompt is %.

prompt variable

The prompt variable is a C shell variable that stores the value of your shell prompt.

protocol

A protocol is a set of rules for exchanging data.

quick substitution

Quick substitution lets you make simple fixes to the most recent command and rerun the result.

recursive listing

A recursive listing of a directory is one that repeatedly displays all subdirectories down the hierarchy, until the last level of the directory tree is reached.

regular expression

A regular expression describes a pattern using literal characters and optional metacharacters known as regular expression syntax.

relative path name

A relative path name is the address of a file or directory, specified relative to the current location.

remote computer

In an FTP session, the remote computer is the FTP server to which you connect. The local computer is the one from which you run ftp.

request ID

A request ID identifies a print request. You can cancel a print request by specifying its request ID.

root directory

The root directory, indicated by a slash (/), is the top-level directory in the UNIX file system.

server

A server is a computer that sends information out to other computers over a network.

shell

The shell is a program that interprets your commands and passes them to the operating system for further processing. You enter commands at the shell prompt (also called the system prompt or command prompt).

shell script

A shell script is a set of commands stored in a file. You can run the file as a program, much like a batch script is run on DOS.

shell variable

A shell variable is a place to store data that is used by the shell.

standard input

Standard input is where a command takes its input from. By default, the standard input is your keyboard. In many cases, if a command accepts a filename argument, the command reads the file as standard input.

standard output

Standard output is where a command sends its output to. By default, standard output is your terminal, but you can redirect standard output to a file (using >) or to another command (using | ).

string

A string is a sequence of characters.

subdirectory

A subdirectory, also called a child directory, is one level lower than the current directory.

symbolic link

A symbolic link is a name that points to another file or directory. The target of the link can reside on another file system.

system administrator

A system administrator is responsible for managing the UNIX system. Common tasks include setting up new user accounts, configuring printers, and backing up data.

tape device

A tape device is any hardware that contains a tape drive for use with storage media.

tar file

A tar file is an archive created by the tar command.

TCP/IP

TCP/IP is a networking feature that divides data into small pieces, called packets. This technique allows data to be passed efficiently within a computer network TCP/IP on UNIX contributed to the growth of the Internet in the 1970s.

telnet

Telnet is a program that emulates a terminal, thereby allowing you to log in to UNIX from any machine.

terminal

A terminal is any device that provides a screen from which you can log in to UNIX.

terminal emulator

A terminal emulator is a program, such as Telnet, that lets your screen behave like a UNIX terminal.

text abbreviation

A text abbreviation lets you add long phrases in text mode whenever you type the abbreviation. Abbreviations are created using the :ab command.

text mode

Text mode is one of two modes of operation in vi. In text mode, you can use your keyboard to add text to your document.

upload

To upload means to transfer data to a remote computer.

user permissions

User permissions are the first set of read/write/execute permissions in an access mode. User permissions apply to the file owner.

utilities

Utilities are small, useful programs. An example is sort.

verbose

When a command uses verbose mode, the command displays more than the usual status information. Many UNIX commands accept a -v option that causes them to run in verbose mode.

wildcards

Wildcards are characters that the shell interprets in a special way. Wildcards create patterns for matching filenames. Examples include ?, *, and [].

word substitution

Word substitution is a technique for replacing part of a command and rerunning the result.WYSIWYG WYSIWYG stands for "what you see is what you get." It means that whatever is displayed on your screen will appear exactly that way when you print it. In other words,the screen displays document formatting--bold, italics, font sizes, and so on. Word processors are WYSIWYG applications. Text editors typicallycannot display formatting graphically, so they are not WYSIWYG programs.

*

The asterisk (*) is a wildcard that matches any number of characters in a filename.

Unix OS Design

.cshrc file

The .cshrc file is a configuration file in your home directory, where you can store custom settings that will be read by the C shell and executed.

.exrc file

The .exrc file is a configuration file that lets you store custom vi settings in your home directory. When you start the vi editor, it reads the .exrc file and runs the commands in the file.

.Z extension

When you run the compress command, the resulting files are renamed to end with a .Z extension/

?

The question mark (?) is a wildcard that matches any single character in a filename.

[ ]

Brackets ([ ]) are wildcards that match a range of characters enclosed in the brackets.