Any filename that begins with a leading slash (/); these always uniquely describe a single file in the file system.

The set of accesses (read, write, and execute) allowed for each of the three classes of users (owner, group, and everyone else) for each file or directory on the system.

This is the official one-word name by which the UNIX system knows you: mine is taylor. (See also account in Hour 1.)

This is the official one-word name by which the UNIX system knows you. Mine is taylor.

The set of vi commands that enable you to specify what type of object you want to work with. The d commands serve as an example: dw means delete word, and db means delete the previous word.

A system set up to respond to ftp queries that does not require you to have an account on the system.

Not any type of domestic dispute, arguments are the set of options and filenames specified to UNIX commands. When you use a command such as vi test.c, all words other than the command name itself (vi) are arguments, or parameters to the program.

The closest directory name. For example, the basename of /usr/home/taylor is taylor.

A file format that is intended for the computer to work with directly rather than for humans to peruse.

An operator that works directly on the bits, without changing neighboring bits.

Changing the location of the bits in memory.

An exact copy of a message, sent without the awareness of the original recipient.

A device driver that controls block-oriented peripherals. A hard disk, for example, is a peripheral that works by reading and writing blocks of information (as distinguished from a character special device).

At its most fundamental, a block is like a sheet of information in the virtual notebook that represents the disk: a disk is typically composed of many tens, or hundreds, of thousands of blocks of information, each 512 bytes in size. See also i-node to learn more about how disks are structured in UNIX.

A saved gopher menu item through which you easily can build your own custom gopher information screens.

A listing of favorite sites for quick retrieval.

A program designed to load hypertext pages and follow hyperlinks.

An area of the screen used to edit a file in emacs.

An exact copy of a message sent to other people. Each recipient can see the names of all other recipients on the distribution list.

A device driver that controls a character-oriented peripheral. Your keyboard and display are both character-oriented devices, sending and displaying information on a character-by-character basis.

The vi commands that begin with a colon, usually used for file manipulation.

When you have a list of items that are listed in columns and span multiple lines, column-first order is a sorting strategy in which items are sorted so that the items are in alphabetical order down the first column and continuing at the top of the second column, then the third column, and so on. The alternative strategy is row-first order.

A shorthand command mapping, with which you can define new command names that are aliases of other commands or sequences of commands. This is helpful for renaming commands so that you can remember them, or for having certain flags added by default.

A list of one or more shell commands that are grouped in a conditional or looping statement.

A mechanism the shell uses to remember what commands you have entered already, and to enable you to repeat them without having to type the entire command again.

The mode in which you can manage your document; this includes the capability to change text, rearrange it, and delete it.

The unique number by which the shell indexes all commands. You can place this number in your prompt using ! and use it with the history mechanism as !command-number.

Each program in UNIX is also known as a command: the two words are interchangeable.

A compiler is a program that takes source code and makes it executable.

This is an expression that returns either true or false.

A notational convention in UNIX that denotes the use of a control key. There are three common conventions: Ctrl-C, ^c, and C-C all denote the Control-c character, produced by pressing the Control key (labeled Control or Ctrl on your keyboard) and, while holding it down, pressing the c key.

A unique number that the C shell assigns to each background job for easy reference and for using with other commands, such as fg and kill.

The image of a command when it executed improperly.

The job that is currently running on the terminal and keyboard (it's the program you're actually running and working within).

A loop where the number of times the loop is run can be known before starting the loop.

All peripherals attached to the computer are called devices in UNIX, and each has a control program always associated with it, called a device driver. Examples are the device drivers for the display, keyboard, mouse, and all hard disks.

A type of UNIX file used to group other files. Files and directories can be placed inside other directories, to build a hierarchical system.

On a hierarchical file system, there must be some way to specify which items are directories and which is the actual filename itself. This becomes particularly true when you're working with absolute filenames. In UNIX, the directory separator character is the slash (/), so a filename such as /tmp/testme is easily interpreted as a file called testme in a directory called tmp.

UNIX systems on the Internet, or any other network, are assigned a domain within which they exist. This is typically the company (for example, sun.com for Sun Microsystems) or institution (for example, lsu.edu for Louisiana State University). The domain name is always the entire host address, except the host name itself.

A shorthand notation for the current directory.

A shorthand notation for the directory one level higher up in the hierarchical file system from the current location.

A configuration file used by one or more programs. These files are called dot files because the first letter of the filename is a dot, as in .profile or .login. Because they're dot files, the ls command doesn't list them by default, making them also hidden files in UNIX.

Although most UNIX systems require all necessary utilities and library routines (such as the routines for reading information from the keyboard and displaying it to the screen) to be plugged into a program when it's built (known in UNIX parlance as static linking), some of the more sophisticated systems can delay this inclusion until you actually need to run the program. In this case, the utilities and libraries are linked when you start the program, and this is called dynamic linking.

Electronically transmitted and received mail or messages.

A process that is not performing the job you expected it to perform.

An unprintable sequence of characters that usually specifies that your terminal take a specific action, such as clearing the screen.

A set of characters that the pattern must not contain.

A file that has been set up so that UNIX can run it as a program. This is also shorthand for a binary file. You also sometimes see the phrase binary executable, which is the same thing!.

A C language construct that had a value. A command that returns a value.

A means of displaying non-Latin characters, such as Japanese, Chinese, or Arabic characters.

When files are created in UNIX, they inherit a default set of access permissions. These defaults are under the control of the user and are known as the file-creation mask.

Most UNIX programs expect to read their input from the user (that is, standard input) and write their output to the screen (standard output). By use of file redirection, however, input can come from a previously created file, and output can be saved to a file instead of being displayed on the screen.

Filters are a particular type of UNIX program that expects to work either with file redirection or as part of a pipeline. These programs read input from standard input, write output to standard output, and often don't have any starting arguments.

Arguments given to a UNIX command that are intended to alter its behavior are called flags. They're always prefaced by a single dash. As an example, the command line ls -l /tmp has ls as the command itself, -l as the flag to the command, and /tmp as the argument.

The protocol used by your computer and terminal to make sure that neither outpaces the other during data transmission.

A synonym for current job.

A set of well-defined steps or a procedure for accomplishing a specific task.

By default, the UNIX file-listing command ls shows only files whose first letter isn't a dot (that is, those files that aren't dot files). All dot files, therefore, are hidden files, and you can safely ignore them without any problems. Later, you learn how to view these hidden files.

This is your private directory, and is also where you start out when you log in to the system.

UNIX computers all have unique names assigned by the local administration team. The computers I use are limbo, well, netcom, and mentor, for example. Enter hostname to see what your system is called.

Specifications within a document that include instructions for loading a different document.

The UNIX file system is like a huge notebook full of sheets of information. Each file is like an index tab, indicating where the file starts in the notebook and how many sheets are used. The tabs are called i-nodes, and the list of tabs (the index to the notebook) is the i-list.

A range of characters that a pattern must include.

A loop where the number of times the loop is run is not known before starting the loop.

The vi mode that lets you enter text directly into a file. The i command starts the insert mode, and Escape exits it.

An interactive UNIX application is one that expects the user to enter information and then responds as appropriate. The ls command is not interactive, but the more program, which displays text a screenful at a time, is interactive.

A synonym for process.

A mechanism for managing the various programs that are running. Job control enables you to push programs into the background and pull them back into the foreground as desired.

The underlying core of the UNIX operating system itself. This is akin to the concrete foundation under a modern skyscraper.

The emacs term for key mapping.

A facility that enables you to map any key to a specific action.

Terminate a process.

Patterns that must occur at the beginning of a line.

The shell you use, by default, when you log in to the system.

A synonym for account name, this also can refer to the actual process of connecting to the UNIX system and entering your account name and password to your account.

This is a sequence of commands that are repeatedly executed while a condition is true.

A file containing one or more email messages.

The To:, From:, Subject:, and other lines at the very beginning of an email message. All lines up to the first blank line are considered headers.

A synonym for mail folder.

For device drivers, the major number identifies the specific type of device in use to the operating system. This is more easily remembered as the device ID number.

Each standard UNIX command comes with some basic online documentation that describes its function. This online documentation for a command is called a man page. Usually, the man page lists the command-line flags and some error conditions.

Analogous to a Control key, this is labeled either Meta or Alt on your keyboard.

Once the device driver is identified to the operating system by its major number, the address of the device in the computer itself (that is, which card slot a peripheral card is plugged into) is indicated by its minor number.

A modal program has multiple environments, or modes, that offer different capabilities. In a modal program, the Return key, for example, might do different things, depending on which mode you were in.

A shorthand way of saying permissions mode.

A modeless program always interprets a key the same way, regardless of what the user is doing.

A multitasking computer is one that actually can run more than one program, or task, at a time. By contrast, most personal computers lock you into a single program that you must exit before you launch another.

Computers intended to have more than a single person working on them simultaneously are designed to support multiple users, hence the term multiuser. By contrast, personal computers are almost always single-user because someone else can't be running a program or editing a file while you are using the computer for your own work.

A command in emacs that requires you to type its name, such as query-replace, rather than a command key or two.

Each character in UNIX has a specific value, and any character with a numeric value of zero is known as a null or null character.

For each account on the UNIX system, there is an entry in the account database known as the password file. This also contains an encrypted copy of the account password. This set of information for an individual account is known as the password entry.

UNIX is split into a wide variety of different directories and subdirectories, often across multiple hard disks and even multiple computers. So that the system needn't search laboriously through the entire mess each time you request a program, the set of directories you reference are stored as your search path, and the location of any specific command is known as its pathname.

The string that represents the access permissions.

The set of accesses (read, write, and execute) allowed for each of the three classes of users (owner, group, and everyone else) for each file or directory on the system. This is a synonym for access permission.

A series of UNIX commands chained by |, the pipe character.

These are what dot files (hidden files) really are: they contain your individual preferences for many of the UNIX commands you use.

Ensure that a message doesn't move out of your incoming mailbox even though you've read it.

The unique name assigned to a print job by the lpr or lp command.

The queue, or list, in which all print jobs are placed for processing by the specific printer.

A program stopped or running within the UNIX operating system. Also known as a job.

A command that repeatedly invokes itself.

A convenient notation for specifying complex patterns. Notable special characters are ^ to match the beginning of the line and $ to match the end of the line.

Any filename that does not begin with a slash (/) is a filename whose exact meaning depends on where you are in the file system. For example, the file test might exist in both your home directory and in the root directory: /test is an absolute filename and leaves no question which version is being used, but test could refer to either copy, depending on your current directory.

A mode of vi in which any characters you type replace those already in the file.

An official UNIX design specification, also known as an RFC.

The directory at the very top of the file system hierarchy, also known as slash.

In contrast to column-first order, this is when items are sorted in rows so that the first item of each column in a row is in alphabetical order from left to right, then the second line contains the next set of items, and so on.

A list of directories used to find a command. When a user enters a command ls, the shell looks in each directory in the search path to find a file ls, either until it is found or the list is exhausted.

The pattern specified in a search.

To interact with UNIX, you type in commands to the command-line interpreter, which is known in UNIX as the shell, or command shell. It's the underlying environment in which you work with the UNIX system.

Most UNIX shells have a convenient way for you to create abbreviations for commonly used commands or series of commands, known as shell aliases. For example, if I always found myself typing ls -CF, an alias can let me type just ls and have the shell automatically add the -CF flags each time.

A collection of shell commands in a file.

Special messages that can be sent to stopped or running processes.

The root directory.

This is the same as standard output, but you can re-direct standard error to a different location than standard output.

UNIX programs always default to reading information from the user by reading the keyboard and watching what's typed. With file redirection, input can come from a file, and with pipelines, input can be the result of a previous UNIX command.

When processing information, UNIX programs default to displaying the output on the screen itself, also known as standard output. With file redirection, output can easily be saved to a file; with pipelines, output can be sent to other programs.

Parameters that you specify on the command line when you invoke the program.

Stop the running program without terminating it.

A shell other than the login shell.

A style of interacting with the World Wide Web, usually for pleasure, where you follow hyperlinks from Web site to Web site.

A file that contains a pointer to another file rather than contents of its own. This can also be a directory that points to another directory rather than having files of its own. A useful way to have multiple names for a single program or allow multiple people to share a single copy of a file.

A command beginning with ~ in Berkeley Mail or the Elm Mail System.

Switch uppercase letters to lowercase or lowercase to uppercase.

Restore a deleted message to its original state.

The specification for a document on the World Wide Web. Usually, it includes a protocol, machine name, and filename.

A set of values that describe the user's current location and modify the behavior of commands.

A synonym for account name.

These are names to label data that may change during the execution of a program.

A process that is stuck in memory and can't free up its resources even though it has ceased running. This is rare, but annoying.

Special characters that are interpreted by the UNIX shell or other programs to have meaning other than the letter itself. For example, * is a shell wildcard and creates a pattern that matches zero or more characters. Prefaced with a particular letter, X—X* —this shell pattern will match all files beginning with X.

The directory where the user is working.

A collection of sites that provide hypertext documents on the Internet.

A particular type of flow control. The receiving end can send an XON (delay transmission) character until it's ready for more information, when it sends an XOFF (resume transmission).

A variable that does not have a value assigned to it.

A terminated process that has not been cleaned up by the parent process.