glossary.htm

the unix power tools

might have been <CODE
CLASS="literal"
>13&nbsp;&#247;&nbsp;3&nbsp;=&nbsp;4</CODE
> (with a remainder of 1).
As computer users, we're more interested in <CODE
CLASS="literal"
>13&nbsp;mod&nbsp;3&nbsp;=&nbsp;1</CODE
>.
It's really the same operation, though.

<EM
CLASS="emphasis"
>Modulo</EM
> is also used in expressions like &quot;modulo wildcards,&quot;
which means &quot;everything but wildcards.&quot;</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-NFS"
>NFS</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
><EM
CLASS="emphasis"
>N</EM
>etwork <EM
CLASS="emphasis"
>F</EM
>ile <EM
CLASS="emphasis"
>S</EM
>ystem. NFS allows UNIX systems and many non-UNIX
systems to share files via a TCP/IP network. Subject to certain
security restrictions, systems are allowed complete access to another
system's files.
<EM
CLASS="emphasis"
>See also</EM
> article
<A
CLASS="xref"
HREF="ch01_33.htm"
TITLE="UNIX Networking and Communications "
>1.33</A
>,
<A
CLASS="xref"
HREF="glossary.htm#GLOSS-TCP-IP"
TITLE=""
>TCP/IP</A
>.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-NEWLINE"
>newline</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>The character that marks the end of a line of text in most UNIX files.
(This is a convention, not a requirement.)</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-NULL"
>null</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>Empty, zero-length, with no characters&nbsp;- for example, a <EM
CLASS="emphasis"
>null string</EM
>.
This is <EM
CLASS="emphasis"
>not</EM
> the same as an
<SPAN
CLASS="link"
>ASCII NUL (<A
CLASS="linkend"
HREF="ch51_03.htm"
TITLE="ASCII Characters: Listing and Getting Values "
>51.3</A
>)</SPAN
>
character.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-OCTAL-NUMBER"
>octal number</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>The base&nbsp;8 numbering system.
Octal numbers are made with the digits 0 through 7.
For example, the decimal (base&nbsp;10) number <CODE
CLASS="literal"
>12</CODE
> is the same as the
octal number <CODE
CLASS="literal"
>14</CODE
>.
<SPAN
CLASS="link"
>ASCII character codes (<A
CLASS="linkend"
HREF="ch51_03.htm"
TITLE="ASCII Characters: Listing and Getting Values "
>51.3</A
>)</SPAN
>
are often shown as octal numbers.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-OPTION-SWITCH"
>option switch</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>Typed on a command line to modify the way that a UNIX command works.
Usually starts with a dash (<CODE
CLASS="literal"
>-</CODE
>).
The terms <EM
CLASS="emphasis"
>option</EM
> and <EM
CLASS="emphasis"
>switch</EM
> are more or less interchangeable.
An option may have several settings, but a switch usually has two
settings:
on or off, enabled or disabled, yes or no, etc.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-PANIC"
>panic</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>UNIX jargon for a &quot;crash.&quot; A panic is really a special kind of a
crash. Panics occur when UNIX detects some
irreconcilable inconsistency in one of its internal data structures. The
kernel throws up its hands and shuts the system down before any damage
can be done. As it is going down, it prints a &quot;panic&quot; message on
the console.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-PARSE"
>parse</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>To split into pieces and interpret.
Article
<A
CLASS="xref"
HREF="ch08_05.htm"
TITLE="Command-Line Evaluation "
>8.5</A
>
explains how the shell parses a command line.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-PARTITION"
>partition</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>A portion of a disk drive. UNIX disk drives typically have eight
partitions, although not all are in use.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-PATH-SEARCH"
>path, search</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
><EM
CLASS="emphasis"
>See</EM
> 
<A
CLASS="xref"
HREF="glossary.htm#GLOSS-SEARCH-PATH"
TITLE=""
>search path</A
>.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-PIPE"
>pipe</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>A UNIX mechanism for sending the output of one program directly to
the input of another program, without using an intermediate file. All
UNIX systems support pipes.
<EM
CLASS="emphasis"
>See also</EM
> article
<A
CLASS="xref"
HREF="ch01_04.htm"
TITLE="Using Pipes to Create a New Tool "
>1.4</A
>.
System V and SunOS also provide &quot;named
pipes,&quot; which are FIFO (first-in/first-out) buffers that have names
and can be accessed via the filesystem.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-PORTABLE"
>portable</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>A program that's <EM
CLASS="emphasis"
>portable</EM
> can be used on more than one version of
UNIX or with more than one version of a command.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-POSIX"
>POSIX</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>An &quot;open&quot; computer operating system that is
similar to UNIX.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-PRIORITY"
>priority</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>A number that determines how often the kernel will run a process.
A higher-priority process will run more often and, therefore, will
finish faster, than a low-priority process.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-PROCESS"
>process</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>A lot of the time, a process is nothing more than
another name for a program that is running on the system. But there
is a more formal definition: a process is a single 
execution thread, or a single stream of computer instructions.
One job may be built from many different processes. For example, a
command line with
<SPAN
CLASS="link"
>pipes (<A
CLASS="linkend"
HREF="ch01_04.htm"
TITLE="Using Pipes to Create a New Tool "
>1.4</A
>)</SPAN
>
starts two or more processes.
<EM
CLASS="emphasis"
>See also</EM
> article
<A
CLASS="xref"
HREF="ch38_03.htm"
TITLE="Managing Processes: Overall Concepts "
>38.3</A
>.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-PROCESS-ID-PID"
>process ID (PID)</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>UNIX assigns every process an ID number (called a PID) when it starts.
<EM
CLASS="emphasis"
>See also</EM
> article
<A
CLASS="xref"
HREF="ch38_03.htm"
TITLE="Managing Processes: Overall Concepts "
>38.3</A
>.
This number allows you to refer to a process at a later time. If you
need to
<SPAN
CLASS="link"
>kill (<A
CLASS="linkend"
HREF="ch38_10.htm"
TITLE="Destroying Processes with kill "
>38.10</A
>)</SPAN
>
a runaway program, you refer to it by its process ID.
The
<SPAN
CLASS="link"
><EM
CLASS="emphasis"
>ps</EM
> (<A
CLASS="linkend"
HREF="ch38_05.htm"
TITLE="The ps Command "
>38.5</A
>)</SPAN
>
command displays process IDs.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-.PROFILE-FILE"
>.profile file</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
><EM
CLASS="emphasis"
>See</EM
> 
<A
CLASS="xref"
HREF="glossary.htm#GLOSS-DOT-FILES"
TITLE=""
>dot (.) files (.cshrc, .login, .profile</A
>.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-PROMPT"
>prompt</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>How a program asks you for information: by printing a short string
like <CODE
CLASS="literal"
>Delete afile?</CODE
> to the terminal and waiting for a response.
<EM
CLASS="emphasis"
>See also</EM
>
<A
CLASS="xref"
HREF="glossary.htm#GLOSS-SHELL-PROMPT"
TITLE=""
>shell prompt</A
>.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-PSEUDO-CODE"
>pseudo-code</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>A way to write out program text, structured like a program, without using 
the actual programming language.
Pseudo-code is usually used to explain a program.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-QUOTE"
>quote</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
><EM
CLASS="emphasis"
>See</EM
>
<A
CLASS="xref"
HREF="glossary.htm#GLOSS-BACKQUOTE"
TITLE=""
>backquote</A
>.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-READ-ONLY-FILESYSTEM"
>read-only filesystem</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>Filesystems are usually set up to allow write access to users who have
the proper
<SPAN
CLASS="link"
>permissions (<A
CLASS="linkend"
HREF="ch01_23.htm"
TITLE="File Access Permissions "
>1.23</A
>)</SPAN
>.
The system administrator can mount a filesystem <EM
CLASS="emphasis"
>read-only</EM
>; then no
user will be able to make changes to files there.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-RECURSIVE"
>recursive</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>A program or routine that re-executes itself or repeats an action over
and over.
For example, the
<SPAN
CLASS="link"
><EM
CLASS="emphasis"
>find</EM
> (<A
CLASS="linkend"
HREF="ch17_01.htm#UPT-ART-7410"
TITLE="The find Command Is Great; The Problem Is Finding How to Use It"
>17.1</A
>)</SPAN
>
program moves through a directory tree recursively, doing something in
each directory.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-REVERSE-VIDEO"
>reverse video</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>On a video display, reversed foreground and background colors or tones.
Reverse video is used to highlight an area or to identify text to be used or modified.

For instance, if text is usually shown with black letters on a white
background, reverse video would have white letters on a black background.
<EM
CLASS="emphasis"
>See also</EM
> article
<A
CLASS="xref"
HREF="ch05_08.htm"
TITLE="Terminal Escape Sequences "
>5.8</A
>.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-SCSI"
>SCSI</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>Small Computer Systems Interface, a standard interface for disk and
tape devices now used on many UNIX (and non-UNIX) systems.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-SEARCH-PATH"
>search path</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>A list of directories that the shell searches to find the program file you
want to execute.
<EM
CLASS="emphasis"
>See also</EM
> articles
<A
CLASS="xref"
HREF="ch06_04.htm"
TITLE="The PATH Environment Variable "
>6.4</A
>
and 
<A
CLASS="xref"
HREF="ch08_07.htm"
TITLE="Setting Your Search Path "
>8.7</A
>.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-SHELL"
>shell</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>A program that reads and interprets command lines and also runs those programs.
<EM
CLASS="emphasis"
>See also</EM
> articles
<A
CLASS="xref"
HREF="ch08_05.htm"
TITLE="Command-Line Evaluation "
>8.5</A
>
and
<A
CLASS="xref"
HREF="ch44_03.htm"
TITLE="What's a Shell, Anyway? "
>44.3</A
>.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-SHELL-PROMPT"
>shell prompt</A
></DT
><DD
CLASS="glossdef"
><P
CLASS="para"
>A signal from a shell (when it's used interactively) that the shell is
ready to read a command line.
By default, the percent sign (<CODE
CLASS="literal"
>%</CODE
>) is the C shell prompt and 
the dollar sign (<CODE
CLASS="literal"
>$</CODE
>) is the Bourne shell prompt.</P
></DD
><DT
CLASS="glossterm"
><A
CLASS="glossterm"
NAME="GLOSS-SLASH"
>slash</A